To grab a wav or mp3 from someone you would have to be able to see what's being played - or know that the person you're trying to get a file from actually has it, with the correct filename. To enable this, go to sounds-> requests-> enable sounds-> accept sound requests-> and check the box that says 'warn if sound doesn't exist'. Then to grab, type !nick nameof wav.wav or !nick nameofmp3.mp3 (where 'nick' is the name of the person you're grabbing from, and 'nameof' is the actual name of the file'). The other person has to have 'accept sound requests' checked too. A word of warning though - I wouldn't personally use this unless I
trusted the person I was grabbing a file from, and even then it's not without risk. If you're looking for a filesharing medium, I'd go for Kazaa or something like that.