10.5, I know 10.6 is even better but either way there are no ATI 5xxx drivers. As for my Laptop, it would be deadly risky to install 10.6 on it as it runs a ATI Radeon Mobility HD3650 and I needed 3 people on IRC to assist me to make it working with hardware acceleration. Plus what the people told me, I am/was the second guy in the entire known OSX86 community who had a working Mobility HD3650 with QE and CI and the native res and giving that up only because VGA out MIGHT work on 10.6 is a big gamble in my eyes.