It is built from old bitcoin code, so the wxWidgets GUI is in there, presumably that should still work on Windows as well as bitcoin's wxWidgets based GUI ever did.
There is also devcoin-qt, but mining cannot be done in the qt version, there seems to be some problem with qt threads or something.
Basically to mine you should use the daemon, devcoind. Again since it is based on bitcoin it should be able to be compiled for windows just like bitcoind was.
I do not do windows, so I am unable to compile for windows. I have no idea how hard windows makes it to compile things, it always seemed to be aimed more at people who do not know how to program or compile so as to make them dependent on other people for binary versions of stuff.
-MarkM-
Thanks Mark, anyone has a compiled version?