Hello,
I just wrapped up a bit of testing on a plugin I slapped together. It is for the Griffin Powermate:
http://www.griffintechnology.com/products/powermate/
Feel free to give it a shot... It can downloaded it from:
http://groomlakelabs.com/grandamp/code/
I don't quite have a web page prepared for it, so I hope the README.txt is good enough for now. The latest version of the plugin is : xmms-powermate-0.0.3.tgz
Any feedback is appreciated, good or bad. Although I already know that someone created some Ruby scripts to accomplish this same task, but I didn't want to deal with additional scripts. I threw this together (Heavily based on the Joystick plugin) for safer control of music in my car, rather than the touch screen @ ~80mph. Have fun, and thanks in advance!