It may well be theoretically possible but I wouldn't advise trying to run a game alongside other applications on a separate monitor. Fullscreen-type games tend to take over the systems resources, capture all the keypresses and mouse movements and generally expect to be the only application running in the foreground. I have a dual-monitor set-up with an AGP card and a PCI card and that works well for most applications but when I play Nexuiz, though I can have applications open on the secondary monitor, I can only use Nezuix on the primary monitor as it takes control of the mouse and keyboard.
If you still want to try, and I recommend having a dual-monitor set-up - it makes life so much easier so long as you remember its limitations, have a look at the Display applet from the Control Panel. For a normal twin-graphics-card set-up you only need to click on the check-box entitled "Extend my Windows desktop onto this monitor" to get both monitors working though I don't know if this will work for your set-up.