x10mp3 is a plug-in for xmms and WinAmp.
The main platform for x10mp3 is Linux. Some of the information on this site is only relevant to Linux versions.
The Boom2000 software is a seperate application, developed by X10, that sends messages to assorted programs like WinAmp and RealPlayer. There are two things wrong with that: 1. you must start a seperate application everytime you launch your Mp3 player, and 2. you must use Windows (blech!)
Since x10mp3 is a plug-in, it is started automatically everytime you run XMMS/WinAmp. x10mp3 has additional features that Boom2000 does not, like balance control, fast-forward/rewind, pause, etc. Also, Boom2000 doesn't run on Linux - x10mp3 does.