Continuing on the topic of troubleshooting the video, I've now managed to get the system to a state where instead of a Windows Protection Error I'm given the option between working video and SoundBlaster-emulation. When SoundBlaster emulation for the Vortex is enabled, the system will simply hang at boot after the splash goes away and the desktop is set to appear. I then have to enter Safe-Mode and disable the emulation. With emulation disabled, everything seems to work, including the sound in Windows. I've tried various combinations of resource settings for the emulation (swapping IRQs and DMA channels) both from Windows and by forcing resource reservation directly from BIOS, but haven't found a setting Windows would be happy with. It all used to work, so naturally I'm - not really baffled I guess, it is Windows after all, but still - I think that may honestly deserve its own thread.

Instead, what I wanted to get some peer guesswork for today was this random visual corruption that has begun to appear sometimes during post:

I initially saw it the first time the system hung and thought the Radeon 9700 had died as a result of my cooling upgrade, but I now know it also occurs with the other video card as well and the Radeon continues to perform when Windows is up and running without issues. I'm wondering if maybe this is a sign of the motherboard acting up, or some kind of inappropriate AGP/memory settings. There is no relationship between the corruption and successfully booting into Windows. That is 100% contingent on whether SoundBlaster-emulation is enabled or not for the time being.

OK, I'm putting the blame for garbled POST-images on memory timings that may have been too aggressive. They were manually set to 2 pretty uniformly, so I loaded Setup defaults and left them at 'By SPD'. Haven't seen corruption since.

Mission accomplished! The Radeon lives and works great.