I think PG for windows is in beta at this point.
Windows Services for UNIX was recently discussed on the AOLserver mailing list. I don't think anyone has managed to get the thread-enabled Tcl compiled on it yet. http://search.gmane.org/search.php?query=Windows+Services+for+UNIX&group=gmane.comp.web.aolserver http://article.gmane.org/gmane.comp.web.aolserver/10826/
I think PG 7.5 is not officially in beta yet, though the PG sources now compile natively on Windows, and nightly binary builds are available: http://momjian.postgresql.org/main/writings/pgsql/win32.html http://www.hagander.net/pgsql/win32snap/
I tried an OpenACS install with a nightly build a few weeks ago but it wouldn't work out of the box and I haven't had time to investigate. I do remember thinking that the error looked more like a 7.4 -> 7.5 incompatibility than a Windows issue.