Microsoft
already makes quite a bit of UNIX functionality available for Windows, as their "Services for UNIX" add-on:
http://www.microsoft.com/windows/sfu/default.asp
As near as I can tell, this product is essentially a UNIX emulation layer for Windows, bundled with a copy of the GNU tools! (In other words, it is Microsoft's answer to Cygwin.)
I find it quite amusing that Microsoft will actually sell you a copy of the GNU C++ compiler! Exposes their whole "Open Source is evil and viral" argument as the FUD it really was, doesn't it?