X is known to have problems with radeon's on macs in general (I have to slightly hack it on my desktop AGP radeon card). Ani Joshi has patches for this and most of his work is supposed to have reached XFree CVS HEAD. Some other people are working on getting it to work on the new powerbook on linuxppc-dev mailing list.
Note that I'm waiting for one of these beasts as well (should be here this week) and I am a debian user, so I will probably post a "fixed" (hacked ?) radeon_drv.o as soon as I get it working. Ben.
