Afaik the album art files are not zip files. I am concerned you may have a virus and hope very much you have anti virus software installed, up to date, and in constant use. It is easy to pick up viruses using Limewire, and a read of this thread is vital.:-
http://www.gnutellaforums.com/showthread.php?t=41432 It tells you about, among many other things, free online virus scans, and Norbies World who are good at sorting out Virus problems.