Does anyone know how I can share music over skype?
You can send files. But as far as sending your signal to them so they can hear what you're playing, you'll have to mess with some recording sources and possibly even need some software that makes a false signal that can be picked up from third party apps like Skype or Ventrillo.
However, some music player software let you change what signal the music is played through thus allowing you to share the same signal as the one you record your voice on via Skype. Try fiddling with Winamp if you're patient enough, otherwise your best bet is google because the process of making it work is tedious and complex to say the least.