[oxelamp]

I don't know exactly if Your video card works as ours (parhelia and p750).
But most likely you have to setup your second monitor to work as a "feature display" and enable "purevideo" or "dvdmax" in matrox control panel.
Then windowed video will be automatically played back full screen in your feature display.
You need Powerdesk HF version to be installed to access purevideo/dvdmax.
Note that pro tools video window must be enabled in your main monitor, though you can scale it down as much as possible.

I hope it helps.