Forum OpenACS Q&A: Yet Another Native Win32 Port of PostgreSQL
Cygwin is still needed to build it, since PG uses bison and other unix tools, but the readme says after that you have a native Win32 PG.
The japanese win32 port basically had stripped out everything that made PG worth, so it didn't go very far in adoption. I don't know if Jan's patches are based on that, or if there are any shortcomings.
While it requires Cygwin to build, hopefully either the PG project or other folks will make pre-built Win32 x86 builds available once it becomes a supported platform (planned, I believe, for 7.4).