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Looks like this is another one of those games where the developers have only had a Win7 machine to test the game on, so they've listed Windows 7 as a requirement.

Has anyone tried running it on Vista, and if so does it work?

And I guess, should anyone else be interested, has anyone tried it with Windows XP, and if so does it work?
This question / problem has been solved by dickesKindimage
This is a late reply but maybe someone still cares:
The game runs fine on XP and Vista