Bah!
I gave up on my ATI X1600 on Vista and bought a new PC, since I'm sick of reporting the bug to ATI that the OpenGL accumulation buffer doesn't work (it uses the front buffer as source instead of the buffer set by glReadBuffer).
Now I've got an nVidia 8600GT. Yay!, you might think. Unfortunately, multithreaded OpenGL doesn't work there. There's some race condition in the driver that means 8/10 times it doesn't display anything.
Both cards with the same EXEs work perfectly under XP.
Anyone know any engineers at either company I can have a chat with? I promise to provide source/examples.
Jim