make sure you can browse the web like normal with your connection. If you can't browse, gnutella won't work.
when gnucleus starts it should connect with two hosts, you can manually enter them and connect that way:
gnutellahosts.com:6346
router.limewire.com:6346
sometimes these are down, or very busy so try again.
Once you connect, they will give you 10 host IP's and disconnect. Those 10 should give you 10 each and on and on, from then on you should start up ok every time from your own list.
You could ask someone to mail you IP's from their host cache and type them in till you get one, but if you give it a chance you should be able to do it yourself.