Hi.
I am on Windows 8, having bought a laptop in early February that runs on Windows 8. It could be due to the fact that it is a laptop, not a proper gaming computer, but I found the game works fine, just a little laggy and it takes at least 2-3 mins to start up, and another 2 mins to actually load a map/mission etc.
I am hoping that an update for SSE fixes this, but again, it could be due to the fact that I am running this game on a laptop.
Hope this helped, Aslas