There's afaik no zip-file you could download. Do you know CVS? If not follow this link
http://www.limewire.org/docs/ddCVS.html. On most (all?) Unix Systems you can copy & paste these commands to download a copy of the LimeWire source code...
cvs -d:pserver:guest@cvs.limewire.org:/cvs login
press enter for password (no password)
cvs -d:pserver:guest@cvs.limewire.org:/cvs co core
cvs -d:pserver:guest@cvs.limewire.org:/cvs co gui
cvs -d:pserver:guest@cvs.limewire.org:/cvs co lib