ATI Win2K vs OpenGL Screen Saver

I’m writing an OpenGL Screen Saver for Windows, and everything works great as a .exe, and as a .scr in Win9x/Me, but when my Screen Saver actually launches as a .scr under Win2K on an ATI Radeon card, what was running at 20fps in the exe, or under Win9x, drops to 2fps…but it’s strange, cause it’s only a problem when it actually launches as a screen saver under Win2K on an ATI Radeon…

Any clues as to what can do other than ban ATI on Win2K?
Anybody know how I can identify the ATI Win2K driver?