I've never bothered checking before which uses more resources as I normally use a couple of pc's if I'm doing stuff that is heavy on the cpu, ie file conversions or video conversions, but I'm down to one working at the moment in this room.
So I got some music on, surfing and some files converting in the background, damn it got clunky, so I decided to check in my task manager which uses the most cpu, seems windows media player uses about twice the amount of cpu to play music than winamp does, shall have a look for a drive with vlc and try that out, also winamp seems to be better quality sound, strange but true.