I have installed the latest version of Cygwin + X11 under Longhorn/Vista Ver 6.0 Build 6001 Service Pack 1,
running under WOW64 on AMD64. Cygcheck says that "Longhorn/Vista (not yet supported!)" but things seem
to work, so far. I have downloaded the lot today, Feb 18, 2009, and the version numbers on X11 are:
xorg-cf-files 1.0.2-7
xorg-docs 1.4-1
xorg-scripts 1.0.1-1
xorg-server 1.5.3-6
xorg-sgml-doctools 1.2-1
xorg-util-macros 1.2.1-1
xorg-x11-base 7.4-1
xorg-x11-bin-dlls 7.4-1
The installation and post-install all went smoothly, but on trying to start X11, xterm, as invoked by startxwin.sh, would say "Unable to load any usable ISO8859 font" and exit. X11 would run though and xterm -fn fixed would come up just fine, sic. I have eventually tracked the problem to... there not being any fonts.dir files in the /usr/share/fonts subdirectories. After I had made these manually with mkfontdir the problem went away.
Looks like a bug in post-install. But... I did not have this problem on XP, on which I had installed Cygwin and X11 yesterday only. So, it seems to be Vista specific.