Just to add a note that I experienced the same problem last week on my iMac Indigo (500 Mhz, 768 Mb RAM). I downloaded the most recent versions of Ubuntu alternate and Xubuntu alternate (the regular ones would not boot) and attempted to install them.
After installing it took a very long time for GDM to load and the screen to be drawn. After login I could move the mouse freely, but after clicking on a menu item the system froze. Only a hard reset was possible. Debian Sarge and Debian Sid don't have the same problem. Sarge is running 2.6.8 kernel by default. I tried Yellowdog on the same box and it didn't have this problem as well. It seems to be specific to Ubuntu. The suggested DRI and FBDev options work fine both in Yellowdog and Debian Sarge/Sid and did not have to be uncommented on my box. -- 2.6.12 and above create 100% CPU with xorg on iMac https://launchpad.net/bugs/22667 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs