The traditional dual-projector mode requires you to have only two displays connected to the pc (the two projectors), no 3rd auxiliary monitor connected (or you'll get detection issues).
You should have one of your projectors setup as the primary windows display and the other projector as a secondary display using windows extended desktop.
This is how all classic dual-projector modes work (old nvidia drivers, DDD drivers, iZ3D drivers, Stereoscopic player, Crysis 2, Avatar the game, etc...)
This technique has a drawback though : the left and right eye views aren't maintained in perfect sync unless you have a professional graphics card with the frame-lock feature.
I recommend using the Eyefinity method since you have a compatible AMD card. It will ensure the left and right eye views are perfectly synchronized even with your consumer graphcis card.
Go to the AMD catalyst control centre and setup your projectors so that they are spanning horizontally with the left eye projector on the left and right eye projector on the right. (you can set them at 24Hz for movies if your projectors support it, or at 60Hz for everything else), save your configuration as presets in the AMD control centre, so that you can switch quickly from one configuration to the other.
Then for movies if you movie is stored side by side, you can then just play it in almost any movie player. You'll just need to full-screen and stretch the picture across the entire screen (not respecting the aspect ratio) and the views should render properly. If your movie is in a different format, then you can use stereoscopic player, it can output side by side at full resolution to match the projectors configuration.
For games, the iZ3D driver has a special mode for such a setup but it's hidden in the config files because it's a highly beta feature (many games have issues with the scaling, with the mouse pointer not working properly, and so on)http://forum.iz3d.com/viewtopic.php?t=5214
Desktop : Intel Core i5-750, 4GB RAM, ATi HD5870, Windows 7 64bit
Laptop : Intel C2D-P8600, 4GB RAM, nvidia 9700M-GT, Windows Vista 64bit
Displaying Zalman Trimon 22" and 106" Passive polarised dual projector setup.
Watch my Stereo3D gaming video footage viewtopic.php?f=3&t=2020