I've been quite happy with my Radeon too, it ran flawlessly under SP1.
This blank screen problem first occured when I installed SP2 last year.
I then uninstalled SP2 again to have a stable system. Due to security
concerns I went back to SP2 3 days again and updated to the latest ATI
drivers (Catalyst is currently not installed) but the problems are
still there. I doubt that ATI would leave this problem unresolved for a
year so it's likely someplace else. There have been very similar
reports in other XP newgroups but no good solutions. One poster
mentioned throttling down the AGP port to 4x, but that's a hack and not
a solution.