Forum OpenACS Q&A: Response to Windows, AOLServer, and OACS
No, I think they actively removed Windows support at version 4; I seem to remember seeing that in a changelog entry from SourceForgeSeveral people have gotten OACS to run on Windows, but not well.
It was stable enough for me only for development. I discovered VMWare (thanks to John Sequeira) and never looked back.
Note there was been some discussion here about compiling late versions of nsd under the Cygwin toolset. That could work, but if one needs to use Oracle, getting the Oracle driver stable under Cygwin might be quite an effort.