Thanks for sharing the xorg.conf file. I added it to my list of working machines on:
http://mac.linux.be/content/xorgconf-files

The xorg above with tty's switching will only work if linux-firmware-(non)free is installed, otherwise it will crash after terminal switching or just hangs on a half broken screen. I can also confirm that it works on debian Squeeze 6.02. So Debian 5 Lenny, Debian 6 Squeeze and ubuntu 11.04 work fine. Although ubuntu and probably debian testing with newer kernel need the "video=offb:off" option in yaboot.conf to disable a conflicting framebuffer, and uncomment the aty128fb in blacklist. See my previous post.

I can also confirm that 1900x1200 is no problem on the pci G3 with debian lenny, probably newer versions and the agp G4 will also work since they use the same xorg.conf and driver. Just add the resolution to my xorg.conf.txt posted earlier and startx

" This was fixed by adding "video=offb:off" to yaboot.conf in the append section, btw this file resides in the boot partition not in /etc/."

can some one do explain how you access this file in order to edit it? I see no way to get into the boot partition in order to edit this file. I found a yaboot.conf file in /etc but editing this did nothing. I also used the enclosed xorg.conf that the member so graciously shared but all it did was to kill my screen completely.
any help would be appreciated. I am running a PowerMac G4 with ATI rage 128 agp card. Stuck at 800x600 resolution

Thanks

edit...sorry but I solved it...by using a custom XORG conf...I am poating it in another place so folks can use it too if they want...thanks