I just went through this exact decision-making process. I bought the Mac because I liked the design of the hardware, though, and have no use for the OS.

Ultimately I bought the Macbook. There just wasn't enough difference in performance to justify the price, and I prefer the smaller size. The macbook with the 2GHz processor runs Windows faster than just about anything. You will NOT have performance issues. The integrated graphics are plenty fast - they will run Vista in the highest-quality mode with no problem. You need 1GB of RAM for both OSes, but do not buy it from Apple - it's horribly overpriced. There's nothing special about it and you cah buy from any PC store (I bought mine in Boulanger, which is like a Best Buy).

Installing Windows is pretty easy. You just download BootCamp from Apple and follow the instructions. The Macbook will restart just like any other Windows PC and installation is exactly the same.

Downsides: the thing gets bloody hot. Too hot to rest on your lap without burning your leg. The keys scratch the nice shiny screen. And it has no right mouse button. If you're going to spend lots of time in Windows you'll want to use a mouse with it (though there is a hack that sort-of works).