I just saw a message by Jan Wieck, of PL/pgSQL fame, to th pgsql-patches list, where he posted patches and a readme on how to build PostgreSQL natively for Win32.
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.
-Roberto