hey you might want to use the so called span-mode for your graphics card settings, if your system shows one screen per projector. This mode handles your three screens as it would be one.
the faq is outdated, you can use span mode in w7 by simply going in nvida control pannel and setting it up. There it is called Mosaic-Mode
You can also download configureMosaic.exe and use the following commandline parameters to activate it:
> cd c:\Path\
> configureMosaic.exe set rows=1 cols=3 overlap=0,0 res=1920,1080,60
This might be handy if you want vvvv or a startup script to set up the span mode.
did this solve your problem?