Clang has complete support of windows (modulo Windows standard library bugs in libc++)
You can download an "official" windows build of clang 3.3 from here: http://www.llvm.org/builds/
It doesn't include libc++ so you'll need to download either that or your standard library of choice. I'd recommend using libc++ if possible, as this is currently the most complete library implementation, although I don't know how well it works on windows.
