look at your key board.
you'll see √
Ω

Stosher is referring to the "command" key when he uses the term "splat", but I don't think that matters because, as you discovered, copy & paste doesn't copy the names of the files (in fact, in Snow Leopard it doesn't even let me copy the results).

However, if you're willing to venture into the Terminal this is not too hard, since UNIX has all sorts of commands for doing exactly this type of thing. For example, here's a command you could use in the Terminal that will create a file on your Desktop called "mp3.txt" that lists just the file names (i.e. without the folder name prefixed to it) of all the files that have a ".mp3" extension anywhere in or under your home folder (but not in any other users' folders, or in any system folders):

find ~ -iname "*.mp3" -exec basename '{}' \; > ~/Desktop/mp3.txt

If you want a separate file with a list of your .wav files, just change the "mp3" parts of the above command to "wav" in both places. If you want a single file with both types of files in it that's a little different, but not much, depending on how you want the the final list. There's also an easy way to sort the results, but I didn't want to make things too complex.

Here's what that command above does:

The "find" is the actual command. The "~" tells the find command to start looking in your home folder. The "-iname" tells find to look for files with names that match the pattern you'll giveit next, and tells it to ignore the case of the file names as it's looking for them. The "*.mp3" is the pattern you're looking for, which in this case is any name (that's the * part) followed by the pattern ".mp3". Note that you need to include the double quotes around the *.mp3 part. The "-exec" part tells find to run the following command on the file names it finds, and the "basename" part is that command. This is used to strip off the folder part of the results. If you leave off this stuff then the output will include the full path name of all the files, starting with "/Users/username/...". I'm assuming you don't want this, since your friend probably doesn't care what folder(s) the various files are in. The funny looking "'{}'" part (that's a single quote, a left curly brace, a right curly brace, and another single quote) is a shorthand that represents the filename the find command found that the "basename" command is supposed to trim. The "\;" part tells the "find" command that this is the end of the sub-command that was started with the "-exec" parameter. The ">" part is the standard UNIX way of taking the output of a command and saving it to a file, and the "~/Desktop/mp3.txt" part at the end is the name of the file you want the results to be saved in.

I know this is a complex looking command, but it's not dangerous and should be relatively standard so it should work no matter what version of OS X you're running. There may also be an easy way to do this in AppleScript, but I'm not an AppleScript guy.

Post a follow-up here if you have any questions and I'll do what I can to help.

Good luck!

Dana