Is this the only display that will be connected to the computer? If not, what's the resolution of the other display? I just spent the last few nights connecting both my HDTV (Olevia 232T 720p) and projector (BenQ MP610) and trying to get them working nicely with each other.
My problem was that I had just upgraded the graphics card in my HTPC to an HD4670 from an HD2600Pro (for the HDMI audio capabilities). However, with the new graphics card installed, my old resolution settings would no longer work. With the new card installed, I can only use the HDTV resolution of 1080i @ 30Hz. All others (while the projector is enabled) result in an, "Invalid Format" message on my HDTV.
In the end, I had to set up hotkeys in order to enable Clone Mode and to disable all non-primary displays, so I can easily switch between watching movies on the HDTV or the projector.