After seeing Renoir's blog post about how he got the Java RepRap Host software working in OSX, I figured I'd give it another try.  I had given up on it and installed Ubuntu on an old PC, but it's kind of slow and I was having issues with 3D applications through VNC to it... anyway, Renoir's solution got me working, but was kind of ugly.  I think I figured out a better way to do it.  Here's the steps:

svn co https://reprap.svn.sourceforge.net/svnroot/reprap/trunk/reprap/host

cd host

./host-package-release

cd release/reprap-mendel-20100620

curl -O http://iharder.sourceforge.net/current/java/librxtxSerial.jnilib

./reprap

Preferences -> Port(name): /dev/tty.usbserial-FTESF4XM

Might need to exit and restart ./reprap

Your port name may or may not be the same, I don't know.  There are a few graphical glitches and I'm not entirely sure if everything is working since I don't actually have a complete Mendel yet, nor have I actually used the RepRap host software before, so I don't know if the glitches I'm seeing are normal or not.  However, I was able to test the electronics, controlled a stepper motor, and was able to load an STL file.  I'm waiting for mouser to deliver the last few connectors I need to wire my Mendel up this week.  I'll find out if it works then.