nVidia GeForce 4 Ti on a 2x AGP board

The manual for the GeForce 4 Ti says that it should be supported by any board that supports at least 2X/4X AGP, which the Gigabyte GA-6VXE+ does. However, when I put the card in, graphics displayed on the screen appear somewhat garbled. (The Blue Award logo has bits of green in it, fonts are mangled in Windows, black pixels follow the cursor around.) Occasionally, the monitor will go idle as if the PC is turned off. I’ve installed the Detonator drivers from nVidia’s website, and this is on a fresh installation of Win2k Pro. I can’t figure out what’s wrong.