With a 8800 nvidia card, download the latest drivers, which you would do anyway.
Right click on either display and select the nvidia control panel. Select the option to configure multiple displays. I think you will want "dual view".
With dual view, both monitors look like one large monitor. You can drag a window from one to the other, and do anything you could on just one monitor. When playing a game, the only main monitor will be used. There may be some games that can use multiple monitors.
I will leave my e-mail up along with some performance monitor on one display while playing a game. If I need to break out of the game, I press the windows pearl button, the game is suspended, and I can do anything I want before resuming the game.
Dual monitors is one of the best things around.