Cannot unmount disk

It is neither black nor gray, it is literally a copy, on a gold DVD-R.

About Installer:
Version 2.1.0 (86.1)

That's all I can tell for now. Maybe I can put the disk in a PC/DVD drive to see more about it.

Here's the readme...sorry, don't know what we're looking for, so the whole thing:

Read Before You Install Mac OS X
Read this document before you install Mac OS X. It includes information about supported computers, system requirements, and installing Mac OS X.
For more information about Mac OS X, visit this website: • www.apple.com/macosx/
For the latest information about using Mac OS X, connect to the Internet and open Mac Help. To open Mac Help, click the Help menu in the Finder and choose Mac Help.
For information about the support available for this product, see the AppleCare Software Services and Support Guide included with Mac OS X.
System requirements
You must have a Macintosh computer with: • a PowerPC G3, G4, or G5 processor • a DVD drive • built-in FireWire
• at least 256 MB of RAM • a built-in display or a display connected to an Apple-supplied video card supported
by your computer • at least 3 GB of disk space available, or 4 GB if you install the developer tools
If you see a message in the Installer that you do not have enough disk space to install Mac OS X, you can deselect items to save space. To deselect items, click Custom Install in the Easy Install panel.
Updating your computer’s firmware
You may need to update your computer’s firmware. It’s best to update the firmware before installing Mac OS X. If you haven’t started the Mac OS X Installer, check the Apple Software Updates website to see if there are any firmware updates for your computer:
• www.apple.com/support/downloads/
If you don’t do this, you may see a message that you need to update your computer’s firmware when you start the Installer. To update the firmware, you will need to quit the Installer and restart your computer using your current startup disk, then check the Software Updates website.
If you have problems with your computer after installing this version of Mac OS X, you might need to update the firmware even though you did not see a message when you installed the software. Check the Software Updates website for recent firmware updates for your computer.
Starting installation
To start installing Mac OS X, insert the Mac OS X Install DVD and double-click the Install Mac OS X icon:
You can also start installing Mac OS X by inserting the Install DVD and restarting your computer while holding down the C key, or by selecting the Install DVD as your startup disk using Startup Disk preferences.
Quitting the Installer
If you need to quit the Installer before you click Install in the Easy Install or Custom Install pane, choose Quit Installer from the Installer application menu, then click Startup Disk to select a startup disk for your computer.
If you have already clicked Install, wait until installation finishes.
Advice about hardware compatibility Installing on a Power Macintosh G3 (Blue and White)
If you have a Power Macintosh G3 (Blue and White) that came with an Apple SCSI hard disk, do not choose UNIX File System (UFS) as the format for the destination disk.
Installing on a computer with a third-party SCSI card
If you have a third-party SCSI card installed in your computer and you cannot start up Mac OS X, attach a disk drive or terminator to one of the card’s ports. If you continue to have problems, try removing the card. Contact the manufacturer of the card for more information about using the card with Mac OS X.
Installing on a computer with a third-party video card
If you have a third-party video card installed in your computer, you may need to remove it before you install Mac OS X. Contact the manufacturer of the card for more information about using the card with Mac OS X.
Advice about installing Mac OS X Erasing and formatting your disk
When you install Mac OS X, you can erase the destination disk you select. In the “Select a Destination” pane of the Installer, click the Options button. Select Erase and Install then choose a format. In most cases, choose Mac OS Extended (Journaled).
Important Do not choose UNIX File System (UFS) unless you need to work with this format. If you choose UFS, Mac OS 9 and all Mac OS 9 applications must be installed on a Mac OS Extended format disk to use them with the Classic environment.
To install Mac OS X on the same disk or disk partition as Mac OS 9, the disk must be in Mac OS Extended format. If it isn’t, quit the Installer and back up your files, then reformat the disk.
You can also partition your hard disk into several volumes before you install Mac OS X. In the Installer, choose Utilities > Open Disk Utility and click Partition. Partitioning the disk erases the entire disk, so be sure to back up your files first.
Installing optional software
Easy Install installs all the software you need to use Mac OS X, but does not install some additional software. If you want to install this optional software or you don’t want to install all the software installed using Easy Install, click Custom Install and select the items you want to install. If you want to install this optional software later, insert the Mac OS X Install DVD and double-click Optional Installs.
Locating the Installer log
When you install Mac OS X, the Installer saves a log of the installation. To see the log, open Console (in /Applications/Utilities), click Logs, then click the triangle next to / var/log and select install.log.
Reinstalling Mac OS X
To reinstall Mac OS X, insert the Mac OS X Install DVD and double-click the Install Mac OS X icon, then follow the onscreen instructions. When you see the “Select a Destination” pane, click Options to select how to install Mac OS X:
• Select “Archive and Install” to save your existing system files, user accounts and their home folders, and existing network settings. The Installer saves files in a folder named Previous System so that you can copy them to an appropriate location later. You cannot start up your computer using the Previous System folder.
• Select “Erase and Install” to erase the destination volume and install a new copy of Mac OS X. If you select this option, you will lose all your files and the software you have installed on the destination volume, so you may want to back it up first. If you select this option, you can choose the format for the volume. In most cases, choose Mac OS Extended (Journaled) from the pop-up menu.
Setting up and connecting to the Internet
If you have an existing Internet service provider (ISP) and you’re installing Mac OS X for the first time, you need to enter your Internet connection information when installation finishes. Be sure to have the information available. If you have problems connecting to the Internet, contact your ISP to make sure you have the correct information.
Advice about using Mac OS X If you have problems starting up
If you cannot start up your computer, insert the Mac OS X Install DVD and restart your computer while holding down the C key. Choose, Choose > Open Disk Utility, then click First Aid to repair your disk.
If you have problems starting up your computer and you have devices connected to your computer such as FireWire drives, USB printers, or external displays, try disconnecting them before starting up again.
Upgrading your applications and other software
For best results with Mac OS X, look for versions of your applications that are built for Mac OS X. Check the Mac OS X website for information about available applications:
• www.apple.com/macosx/
If you cannot find Mac OS X versions, upgrade to the latest Mac OS 9 version to use with the Mac OS X Classic environment. Check with the manufacturers for the latest updates.
Using POP email accounts and On My Mac mailboxes in Tiger and Panther
If you have a shared home folder and you access a POP email account using Mail in both Mac OS X Panther and Mac OS X Tiger, you will not see messages that you retrieve in one version when you switch to the other.
As an alternative, you can deselect the option to remove copies from the server after retrieving your messages. To change this option, open the Accounts pane of Mail preferences and click Advanced.
You will not see messages saved in a mailbox on your computer when you switch from one version to another. To avoid this problem, use separate home folders for each version of Mac OS X.
Your IMAP account will synchronize automatically when you switch between Mail in Tiger and Panther.
© 2005 Apple Computer, Inc. All rights reserved. Apple, the Apple logo, FireWire, Macintosh, Mac OS, and Power Macintosh are trademarks of Apple Computer, Inc., registered in the U.S. and other countries. PowerPC is a trademark of International Business Corporation, used under license therefrom.

I have my Macbook Pro connected by firewire to the iBook. The iBook is in target mode. I am partitioning the drive. I figure 2 parts, one for the OS, one for everything else.

How much do I need for the OS? Seems like I saw 4.x somewhere in all this. Is 5gb enough?
What are typical names for the OS partition and the not-OS partition?

Ok, no partition.

So I did that, then started a one-pass erase. It said it would take 27 minutes, so I left, came back. There's nothing saying 'done', but there's no error messages, so I guess it finished. Now what?

APM partition map ... don't know. How do I tell?

fyi, I got to step 8 of the formatting & partitioning instructions you linked to.

Name : AAPL FireWire Target Media
Type : Disk

Partition Map Scheme : GUID Partition Table
Disk Identifier : disk2
Media Name : AAPL FireWire Target Media
Media Type : Generic
Connection Bus : FireWire
Connection ID : 1007152630408624
Device Tree : IODeviceTree:/PCI0/PCIB@1E/FRWR@3/node@393fffec525b0/sbp-2@4000
Writable : Yes
Ejectable : Yes
Location : External
Total Capacity : 20 GB (20,003,880,960 Bytes)
S.M.A.R.T. Status : Not Supported
Disk Number : 2
Partition Number : 0