try downloading a gnutella.net file here:

ftp://whitedragon.dyndns.org/gnutella.net (might not be available all day long but should be online most of the time) and copy it into your LimeWire folder (the one, that contains the LimeWire.jar file).

This should help. If it doesn't there's a problem with your connection, i.e. you could be behind a proxy.