MP3 and Windows Media (WMA) are already compressed. Changing the
extension will make the music file inoperable. You can cut the file
into pieces to email them with below program. Your party on the other
end will need the program also to put it back together. Some ISP's (Internet
Service Providers) will allow files to be sent up to 10Mb but your recipient
may not have that option, check yours and your friends.
Free File Splitter (600Kb)
http://www.filesplitter.org/