First, you might have done a search through the posts, since this is an issue that has been handled time and time again.

Make sure in internet preferences and in File Exchange that iTunes, and not QT, is set for mp3 (and MP3 just in case).

If Limewire still overrides these preferences, there is a little freeware program called iTunes Associator at versiontracker.com which will automatically change file type and creator to iTunes. You can do this yourself, of course, with Norton's FastFind or ResEdit or some other program that can change the resource fork of a file.

iTunes can play a QT mp3. Just drag to the iTunes library window. The tags, however, will likely be shortened, so it's better to change the file to iTunes by one of the methods described above.