AGP window?
Make sure the AGP window setting in the BIOS is not larger than than the video card memory.
If you have a 64M video and tha AGP windows is 128M windows can go off in the weeds on a regular basis, crashing programs, but surviving. It appears to think there is a second screen (existant or otherwise) sometimes.
A simple terst for this is to put an explorer wind on the screen, then using the bar at the top of the window, drag it around the screen rapidly without overlapping the edges of the screen. So far so good. No start dragging the window further and off the edges of the screen by heaps.
Does it have dificulty redrawing the window while you are off the screen?
ie. You get multiple immages not redrawn in a timely manner.
If so look further for AGP window settings.
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.