After struggling and trying a ton of different things, I finally tried your kexts, and to my surprise they WORKED. Thanks a ton for posting these, they were a lifesaver!!

What I did was delete ATI* from the /system/library/extensions directory (after making a backup of course), and then copied your kexts over the ones that currently existed. (Of course, I went through the whole process of chmod and chowning the files, and removing extensions.mkext)

After that, I had things working but with no 3D acceleration, so I reinstalled the ATIRadeonX1000* files back into the extensions folder, and the ATIRadeonGLDriver.bundle as well, and everything started working perfectly then.

I'm running the iPC 10.5.6 release on an AMD Turion 64 2.2ghz, with an ATI Mobility Radeon x1600.