I have released a snapshot of the current MiKTeX 2.5 source tree:

http://prdownloads.sourceforge.net/miktex/miktex-2.5.2045-snapshot.tar.gz?download

The source tree can be used to build the package manager (MPM) for Un*x systems. The prerequisites are:

• ANSI-compliant C++ compiler (e.g, g++ 3.x)
• CURL libraries