Have your mp3 files changed to .exe? Are the files all the same size? Are they 408KB or 408kb?? Do you have an extra folder in your library (maybe at the bottom of the list) that you didn't create? If you do have a weird folder...is it called "_"?? Does it contain anything (maybe .exe or .zip files)?

I think you have a virus of some sort. Please go to one of the sites below & follow their instructions for posting a HijackThis log (we can't read the logs here).
http://www.spywarewarrior.com/index.php
http://www.castlecops.com/forums.html
http://forums.spywareinfo.com/index.php?showtopic=79038

It would be a HUGE help if you could let us know what they say...this thing is becoming a problem.