After countless tries and OSX reinstalls, I finally managed to get QE working on my Radeon HD 2600 Pro AGP using iDeneb v1.3 10.5.5. I deleted all the kexts that started with ATI and installed the older 2600 Pro AGP easy-install package from insanelymac.

My OSX became unstable after that. I get occasional kernel panics, especially if you minimize your windows alot and also many applications, like Safari, Spotlight and sometimes Finder crash constantly. At some point Safari became unusable. DMG mounter is not working at all, so I can't mount dmg's and have to use pacifist. I checked the info.plist in the ATIRadeonX2000.kext and the device id 9587 is there. Also, my video card is still detected as Radeon HD 2600 XT and also as PCI and not AGP. AGPGart was included in that package.

Does anybody have any idea what's going on?