There are Windows binaries of AOLserver 4.0 beta 8 available at http://empoweringminds.mle.ie/openacs/4/ Starting from my distribution and documentation is a *much* easier way to install OpenACS on Windows than starting from the AOLserver sources. I haven't been publicizing the beta build's existence because I don't really have time to support it, but once AOLserver 4.0 is final, the Windows binaries and installer will be available on SourceForge.
Native Win32 PostgreSQL is due with 7.4 - it has been held up but might be out at the end of the summer. I'm hoping it will have a nice installer like the one for pgAdmin II. So with a little more time and work, Windows will be a first class platform for OpenACS, but as Andy suggested, we should probably put up a warning in the meantime.