Welllll, one can run Cygwin on Windows systems; I have it running on
Win2K-SP4, WinXP-SP3 and Vista=SP1. Full X11R6, xterms, gcc, even
my UNIX/Linux astronomy programs (XEphem, etc), etc all on Windows. :-)

Cygwin is free (<http://www.cygwin.com/>), and is often the only way
to get-around and/or fix Windows-related problems (typically owner
or file protection ones). You can even "play" with the Windows
registry in Cygwin via /proc/registry :-)

If you sat down at my keyboard, you'd really have to look hard to
realize you're facing a Windows system and not UNIX or Linux. Cygwin
is the only thing that makes Windows palatable to me.