Sorry to hear about all your computer woes buddy! but I am running my 9800 se softmodded to a pro (using the regular Cat drivers which are just modified with the Patched ati2mtag.sys file) on the exact same board as you but I am currently running the original 1003 MB bios. I can't speak for others who may be running 9800pros with the newest 1008 MB bios so I don't know if this may be the problem.
However to try to narrow the focus to the problematic element here, you could try 1stly:
1.Clean Install of WinXP CD only. Don't install any more Win. updates just yet.
2.
VIAHyperion4in1v4.49 drivers which I have found to be very stable.
3. A7V8x-x onboard sound drivers
3. A7V8x-x Lan drivers
4.DirectX9.0b
5.Windows Media Player 9
6. Cat's 3.10 very stable for me on every game I've played so far.
I don't normally install the all in one Cat. package. I install the Display Driver then the Control Panel just to make sure of a more controlled install.
If this install goes fine then go and update the critical Win. updates only. If it all gets scewed up after that then the problem may be in something Windows is installing during the update session.
You could also try an Nvidia based card to see if the same thing happens. Borrow a friends card if he/she will let you, just to see for yourself. You could also try changing processors just to see if that has an effect on the stability.
To be honest I have tested my A7V8X-X with Nvidia based cards and ATI, this MB adopts both AGP cards very well.
My 9800 is built by ATI card though I don't think that should have any baring on any compatibility issues.
Providing all of your components are known by you to be working previously ie.Ram and the rest... then maybe you have a faulty MB. It does sound a little weird after all that you have tried a Sapphire Radeon 9600 pro which produced the same problems.
Good Luck!
