Yes, actually it's a pretty common issue. The solution is to change the multi-monitor display mode (there's 2 options, can't remember what they are called) somewhere in the settings dialog. Also there's a multiple display performance option somewhere under 3D settings you may want to check if it's set to single display or multiple.
I can check exactly where the options are when I'm on my gaming machine later, on my laptop right now with an ATI card.