I've done some installs of PostgreSQL 9.0 64 bit on Windows Server 2008 R2 Standard.
When I connect to these instances, PGAdmin complains of the following:
The server lacks instrumentation Functions.
Apparently one is supposed to use the "official" pgInstaller program to install contrib modules in Windows PostgreSQL installs, including the server instrumentation.
However, the pgInstaller is only being maintained up to the PG9.0 RC, not the latest 9.0.1 version.
Given that, how do I get non-default contrib modules installed?
Uh, where did you get the idea that it's only maintained up until 9.0 RC? It's most definitely available for 9.0.1. Go to http://www.postgresql.org/download/windows, and you'll find it.
That said, installation of contrib modules is covered in the documentation at http://www.postgresql.org/docs/9.0/static/contrib.html. If you're building with mingw, that should just work. If you're building with msvc, then skip the build steps - they are always built on msvc - and just do the install/load step.