If you've attempted to upgrade from 10.2 to 10.4 and you've hit a brick wall with the fsck and Open Firmware voodoo, it seems to me that you should do the following:
** NOTE: Installing a new operating system introduces the risk of data loss. Make sure you have backups. Proceed at own risk. **
1. Boot from the 10.4 Install Disc. To do this, turn your machine off. Then turn it on while holding down the mouse button. The tray should open. Put in your 10.4 Install Disc.
2. Hold down the power button until the machine turns off.
3. Turn on the machine and hold the 'C' key to boot from the CD-ROM disc.
4. Look for the "Options" button near the bottom of the screen. I can't remember exactly when it shows up. Perhaps it's after you select the hard drive to which you wish to install.
5. Click said Options button.
6. Select "Archive and Install". This will archive your current (likely messed up) operating system and install Mac OS X "Tiger".
BobW, what do you think?
Doug