You can do all sorts of things with the Raspberry Pi -- and that's exactly the point, because it's a tinkerer's budget dream machine. Running Windows 7 on it, however? That's a little trickier, given its ARM underpinnings -- but there's always a way.
The way in this case is by using the Pi as a thin client and remote desktop for an existing Windows 7 machine. It's one of those ideas that sounds entirely obvious when stated, but still takes a proof of concept to show that it works, and that's exactly what VirtualBigBANGTheory's done.