Try the VLC media player. It can play a lot more than QT or iTunes.
http://www.videolan.org/vlc/
If you can play them with VLC, you know that they are OK files. Maybe some other app can do a "Save As..." with them? Sorry that branched off into nowhere.
Since you can play them, you know that the files are still ok and not corrupted or anything. If you know what the original file extension was, you can try renaming the files to have that extension. Sometimes that helps. If you don't remember the original extension, try renaming the files to have no extension. Maybe OS X will see the files as having the right extension.
Cheers,
Ilya
PS. If nothing works, you can email me one of them and I can try and see if I can make it work. I have lots of audio apps and stuff that can usually convert files to make them readable. Let me know if you're interested.
iMac 20 inch 2.0 GHz Core Duo 250 GB HD 512 MB RAM Mac OS X (10.4.8) iPod video 30GB Black Silver iPod Mini 2G 4GB