Do you have Visual C++? If so, it is possible to compile psql as a native Windows client. There are instructions online at
http://www.postgresql.org/idocs/index.php?install-win32.html
I'm not sure we have enough information to pinpoint your problem.
What version of PostgreSQL are you using? What version of AOLserver? Are you using a nightly tarball, CVS checkout, or released version of OpenACS? Also, what is happening immediately before you get this error? (Could you post sections from PostgreSQL, the AOLserver log, the webpage output, ...)
I'm collecting information for an OpenACS on Windows webpage (http://empoweringminds.mle.ie/openacs/) so I'm definitely interested in your installation experience.
