I am currently implementing an X/Window display server under win32. Just for fun. I do not expect you to share my idea of fun.
The reason why I am implementing such a beast is that for Windows (win98/winNT/Win2K/WinXP/Vista) there exists only two types of X/Window display servers:
So far most x/window-programs work, including twm, mwm and sawfish, mozilla, gedit, etc. I have italian, danish, uk, us and hungarian keyboard layouts working. Font translation works reasonably (there is a semantic gap between the X/Window system and Windows). The selection/clipboard integration is smooth. I have also implemented a few extensions (BIG-REQUEST, SHAPE, SECURITY (partial)). It now features an embedded window manager so you can run it in "root-less" mode.
If I get it to work properly it will either become a free product that
performs well, or an inexpensive commercial product.
It is now available via a reseller WinXServ (by BitBerry).