"WARNING Bison install not found, or unsupported Bison version."

I'm trying to build PostgreSQL 8.2 on Windows XP PRO. I've already
downloaded and configured all the dependencies, including bison and flex.
However, when I try to make it I receive the following error: "WARNING
Bison install not found, or unsupported Bison version.
Attempting to build without." even though bison and flex are installed!
(the latest version from gnuwin32).

I'm trying to compile it with VS2005 (src/tools/msvc)

Any feedback would be much appreaciated,

Marcelo.