http://www.rdesktop.org

It works pretty sweet, but I couldn't get it to work with a w2k server that
had 128-bit encryption enabled on TS.  It works with no encryption, and
apparently 40-bit(though I haven't tested the 40-bit).

A good test server to connect to is scylla.odyssey.securewave.com (don't use
the -l option).  SecureWave set it up so people can test their software, so
it's ok to use it.

Jay