powerpc g4 leopard os x re-install without dvd

put the leopard install dvd into the imac and reboot the imac in target mode (reboot it and hold "t" at the chime). connect it by a firewire cable to the g4. then reboot g4 and hold option at the chime. it will boot you into startup disk manager. one of the options there should be to boot from the dvd sitting in the dvd drive of the imac. choose it and proceed with the install.

You have to use another PPC Mac with a functioning optical drive. That means your PowerBook. The PB must have at least 512 MBs of installed RAM.

With both computers turned off connect a Firewire cable between them. Boot the PPC G4 into Target Disk Mode. Boot the PB normally from the Leopard installer DVD. After the installer loads select your language and click on the Continue button. When the menubar appears select Disk Utility from the Utilities menu. Select the drive entry (mfgr.'s ID and drive size) of the PPC G4 from the left side list. Click on the Erase tab in the DU main window. Set the Format drop down menu to Mac OS Extended, Journaled then click on the Erase button.

After formatting has completed quit DU and return to the installer. Proceed with the installation. When you reach the point where you select a target volume be sure to select the volume for the PPC G4.

There's two variants presented by other posters. I think VK's method is a bit friendlier than Kappy's, unless I am misunderstanding something. The thing is, if you install to your G4 in TDM from another computer the installer will think you are installing for the other model computer onto an external drive (namely the G4). That's why Kappy says use the PPC book, because if you boot the installer on the Intel Mac it will think you want to install an Intel version and that won't work on your G4.

With VK's method the other computer is just seen as a borrowed optical drive and when the installer boots on the G4 from the borrowed optical drive it will think (correctly) it needs to install on a G4. It doesn't matter what other computer is used as long as it is TDM capable.

Anyway, that's my understanding of how this works. I suspect either method will work but using the one where it is the G4 booting to another computer's optical drive is a bit more flexible and makes sure the installer sees that it is installing to a G4.

Are you doing this?

"Start up the target computer and immediately press and hold down the T key until the FireWire icon appears. "

[How to use FireWire target disk mode|http://support.apple.com/kb/HT1661] includes description of hardware and software requirements.

[What to do if your Mac doesn't enter FireWire Target Disk Mode|http://docs.info.apple.com/article.html?artnum=75414], also read about [Open Firmware Password Protection|http://www.apple.com/support/downloads/openfirmwarepassword.html] which can disable Target Disk Mode.

[Technical Note TN 1189|http://developer.apple.com/technotes/tn/tn1189.html#TargetMode] - driver details for TDM

You are sitting there holding down the T key until it completely ignores it and boots up normally?