No pgxs.mk with win32 binaries

Hello list,

I'm trying to build the PL/R module on Win32 with PostgreSQL 8.3. I've
done this before with no trouble using several 8.2.x versions of
PostgreSQL (from the win32 installer). However, now that I'm trying to
update things for 8.3, it seems that the pgxs.mk file needed by the PL/R
Makefile is not included with the PostgreSQL 8.3 installer (PL/R is
looking for this file in this location:
c:/progra~1/postgresql/8.3/lib/pgxs/src/makefiles/pgxs.mk). I checked
in the other zip packages listed on the win32 downloads page, and it's
not in either of those. Are these files no longer part of PostgreSQL
as-of 8.3, or might they be downloadable from some other location?

Thanks for any suggestions,
Mike