Can I bring my own MP3 music files [iPod] and play them in a class?

No. Unless you have the written permission of the copyright owner, you may be in breach of the terms and conditions of use under which the MP3 music files were purchased i.e. for personal use. The University Music licence does not cover downloadable music within the repertoire, even if purchased legally. If the MP3 files are recordings from a radio program, they are covered by Screenrights and can be used with the appropriate notice (see FAQ18).