you can buy software to undelete things, assuming you haven't done anything since he deleted it.
You see, when you delete something (not just put it in the recycle bin, but actually delete it) the information is still on your hard drive, until it is overwritten by something else. Its really hard to know when it has been overwritten, but to be safe, its best to just shut it off and do nothing. The more stuff you save, access, etc. the more the chance of a full erasure.
Now, there are programs available that allow you to undelete. I have never used any of these programs since the days of DOS, so no gaurentees. Go to somebody elses computer to download this:
http://www.download.com/PC-Inspector...ml?tag=lst-0-5
burn it to a cd or put it in a usb flash drive (it wont fit on a floppy disk) and install it on your computer (unfortunatly, there is a risk you could lose some of your deleted music by installing this, but short of other options....)
It should be self explanatory from there.
good luck