head over to the XBMP website and download the tutorial. Here's a link if you are being lazy
http://www.xboxmedia.../info_howto.htmAnd since i am feeling good today, i'll help you out. Open your config.xml file and scroll down to the part that has music. Find HDD and you should have the directory set to e:\music. Just go ahead and change that to where the MP3s are stored.
I've had XBMP on my box for a while, but never got around to making it work. It took about 2 hours, and that includes transfering like 3 gigis worth of media to it. I gotta say i am really impressed and i can't believe i didn't get it work earlier. Mad props to the creators