I had visions of monitors fighting when I read the title...ho hum.

I haven't seen this sort of problem since the days of yore when dual head was a new technology and matrox a viable gaming card In those days it was down to the fact that there would be an inadequate RAMCDAC on the 2nd port... suitable for 2D display but not 3D Accelerated.

Unfortunately I don't know vista from adam so can't offer more useful information.