I only have X850XT PCI-E and X800pro AGP(R420), so my experience may not work for you. When I installed CATALYST 6.2 for X850XT PCI-E on GA-K8A480M-9(ATI RS480 + Uli M1573), manually update resulted in an installation failure after reboot, just like what you encountered. I tried to install the driver by running Setup.exe in subfolder "6-2_wme_dd_cp_30314\Driver", and I failed again. Finally I let CATALYST 6.2 handle the installation and completed without any problem. I need to install CATALYST 6.2 first before downgrading driver. If I install CATALYST 5 directly, an error message appears when entering Win98se normal mode, and Win98se stops working. I also use X800pro AGP(R420), but it works well with CATALYST 4.11~6.2. Compared with X800pro AGP(R420), the installation of X850XT PCI-E is troublesome Besides, ATI supports R481 since CATALYST 6.2, and R480 since CATALYST 5.2. That means X850XT AGP may have more unknown compatibility problems than PCI-E ones.