For FSX, go here:
http://www.matrox.com/graphics/en/suppo ... sgu/ and download the surround game utility. Run that and it sort of does the rest for you. Dont forget to say yes when it asks to put an icon on your desktop, it replaces your normal FSX icon, and will run it in the right mode to cover all your monitors.
I went into the management settings and set the "fullscreen expand" setting so that it will activate on pressing CTL and clicking maximise button. Also, go into Bezel management in Powerdesk, and adjust it so that the lines match.
Dont forget to check your settings in FSX so that the resolution matches your monitor setup. I think mine did it automatically, but worth a check anyway.
Hope this helps.