FOLKS... PLEASE... before you post, ask youself... did I answer the question asked? If not, then please shut up. A comment like "Why would you want to do that" should be translated as "I don't know how to do that, but I'm starved for attention and want to see my name on the screen."
I've tried for hours and hours to get dual monitors to do what they SHOULD be able to do... that is put different output on two screens consistently. It just doesn't work. It has to be addressed at the engineering level. As soon as one screen uses "full screen mode", all bets are off.
For example, just pop in a CD or play an MP3 w/ Windows Media Player w/ the visualization on. All will work fine as long as it's in a window, but once you put it in full screne mode, the mouse/pointer is unavailable and your 2nd monitor either blank or funky w/ neative images of your desktop.
The whole dual screen is clearly a work around. They're not taking it seriously at the design stage.