Q: how to reset to factory spec

First, you need to verify if the machine will run snow leopard.  you need an intel machine to run snow leopard.

You may want to post machine info.

blue apple > about this mac > more info button. Click on the hardware line. It has a little triangle in front of the word hardware.

Leave out the serial number.

Example:

Machine Name: iMac

Machine Model: PowerMac4,1

CPU Type: PowerPC 750 (33.11)

Number Of CPUs: 1

CPU Speed: 600 MHz

L2 Cache (per CPU): 256 KB

Memory: 768 MB

Bus Speed: 100 MHz

Boot ROM Version: 4.1.9f1

--------------------------------------------------------------

Get the Mac to set up  an additional administrative account.  You can then change the password on your old account.

Start with your computer power off.  Hold down command-s. Power on your computer.  

Type in the following:

The first two commands will depend on your release of Mac OS X.  Look at what is typed out in the console to determine the exact format.

# Type the follow two instructions to access the startup disk in read/write. Press return after each command.

# in case of partial success repeat this command until errors go away.

/sbin/fsck -fy

/sbin/mount -uw /

cd /var/db

pwd

#List all files. The l is a lower case L.

ls -a

#The move command acts as a rename command in this format.

mv -i  .applesetupdone .applesetupdone.old

# reboot  your mac

shutdown -r now

Once you've done that the computer reboots and it's like the first time you used the machine. Your old accounts are all safe. From there you just change all other account passwords in the account preferences!!

Limnos adds detailed explainations:

http://discussions.apple.com/message.jspa?messageID=8441597#8441597

The above the idea came from a post by JoseAranda at September 9, 2006 3:48 AM

http://www.askdavetaylor.com/how_do_i_reset_my_mac_os_x_admin_root_password.html

You will need to scroll down to see this post.  Search for applesetupdone

This method is mentioned in an apple support page without giving an explanation.

Once you have a new administrative account, you can change the password of your old administrative account

blue apple > System Preferences > Accounts

Reformat the hd then install Snow Lepard.  You do not need to install the original software.

--------------------------------------------------------------

Format a disk using the installation DVD

To format  the startup drive, you will need to run disk utility from your installation DVD.

This article  will tell you how to get to disk utility.  Once in a disk utility, you can go and format the disk.

http://support.apple.com/kb/TS1417

To format your startup drive, you will need to run disk utility from your startup DVD.
Mac OS X 10.4: About the utilities available on the Mac OS X 10.4 Install DVD

http://support.apple.com/kb/HT2055

How to run disk utility from your startup DVD.

1. Insert your  startup DVD  into your reader.  Power down your machine.  Hold down to the c key.  Power on your machine.  This will bootup your startup DVD. ( Alternatively, you may hold down the control key, this brings up the startup manager. Click on the desired volume. Click on the right arrow. )
2. This will bring you to a panel asking you for your language.  Pick your language.
3. 
   
   
4. You you come to the Install Mac OS panel.  Do not install.
5. Click on Utilities menu item.  This will give you a pulldown list of utilities.
   
   
6. Click on the disk utility.

7. Start up disk utility.
   On the left pane view, you will see a list of all your disks.  Click on the external  disk.
   Click on the partition tab.

   
   

   

   
   
   

8. You will now see how your external disk is currently set up.  Fill in the information as appropriate. You should pick Mac OS Extended (Journaled).

More details on formatting.
http://www.kenstone.net/fcp_homepage/partitioning_tiger.html