I guess now would be a prudent time to ask (should have asked it sooner), do you want the displays mirrored (showing the same thing on both)? If you do, it should be as simple as (assuming Windows 7) right clicking the desktop and going to screen resolution, selecting the second display and choosing Duplicate These Displays.
If that is not what you want, you may have to look more closely into a hack of somekind. Apparently, somewhere along the transition from XP -> Vista -> 7, the ability to span just two displays was removed (at least for nVidia, don't know about others). If you can't find a hack, I would just stick to one display for games (or go the mirroring route).