It looks like the magic trackpad does indeed
work with windows, though without multitouch/gesture support, it's a bit lacking. I'm guessing that Microsoft will add multitouch and some gesture support with their new interface, hopefully rolling in a good deal of their Microsoft Surface technology.
As for the trackpad, that's Apple's problem to support. Microsoft could have generic drivers, but since it's a specific device, it will fall to Apple to come up and maintain driver support... Hopefully once Windows supports multitouch they'll release their drivers more freely without needing to work around the system, but I'm not keeping hopes up.
In general, I'm with Southrend for the overall experience; basically using the Win8 touch interface if you're on a platform that this makes sense, but otherwise using the classic Win7 UI designed for mouse and keyboard. Microsoft said that they're keeping in the theme of Win7 vs prior OS updates in that they're planning on not needing extensive hardware upgrades (if any), so I'll give Windows 8 a shot once it comes out.
