I'm still running MacOS 8.6, so I don't have iTunes, but here's a couple things that might help....
Do the files end with the .mp3 extension? I've seen lots of filenames get truncated after downloading onto my Mac. Try renaming them slightly so they end with .mp3, and maybe iTunes will recognize them?
The other thing you could do is to use SoundApp to convert from mp3 to aiff. It's a top-notch freeware program, and it doesn't have a problem recognizing the files with their truncated filenames: http://www.versiontracker.com/morein...id=4124&db=mac