You need a gnutella.net file to connect:
ftp://whitedragon.dyndns.org/gnutella.net
copy it into your LimeWire folder (I don't know which folder that is on Macs, but it's the one containing your LimeWire.jar file) and start LimeWire. - If you are using LimeWire regularly, you only have to get a gnutella.net file once, since LimeWire will update it, when finding new ultrapeers to connect to.