Don't know anything bout Win7, but maybe give this a try...
On the in-game options screen, try putting a check next to "Windowed Mode". If you run the game at the same resolution as your desktop you probably won't see any difference in the game, but you might be able to use Alt-PrtScrn to shoot a picture of the active window.
I had no probs with PrnScr in XP or Vista32 or Vista64... I'm hoping MS didn't decide to reinvent the wheel with Win7 PrnScrn. I've seen what they've done to "improve" Office 2007 and I shudder to think what unbroken thing they want to redefine for us next.
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