There is a specification for the RMP file format, but I have not read it very carefully. I just wrote a script that happens to work with Emusic. It might even work with other RMP files. If it doesn't, I'd be interested in hearing about it. Actually, I already had to fix one of the creative liberties taken by the emusic team, namely that "&" is not supposed to occur in XML files but does in theirs.
It's pretty simple to use. You run it like
./getrmp.py myrmpfile1.rmp myrmpfile2.rmp myrmpfile3.rmp
and it will go on its merry way, downloading all of the files,
printing progress reports. It creates a directory with the name of the
album and puts all of the files in there. It has a little bit of error
handling, but it should be enough.
It requires the PyXML package. This comes with Python 2.0 and up (I think) and must be downloaded separately for Python 1.5.
Anyway, here is the file. Here is a compressed version.