It's not that LimeWire is risky in itself (in fact it's a pretty good P2P application IMHO), but it connects to the Gnutella network (Gnutella1 for Shareaza) which is entirely decentralized, so there's not much one can do to prevent spammers from flooding the network with junk. The same also applies to other decentralized networks and P2P clients, including Shareaza. Basically you should use an antivirus (The free edition of Avast does a good job for me), as well as a security filter and check files on Bitzi (right click on a search results > Web Services > See Bitzi Ticket) to see other users' ratings to limit the risks. You may also use a little trick to avoid spam: let's suppose you're looking for "Great Speeches - Martin Luther King Jr. - I Have A Dream". Search for "Marthin King Luther Dream Have", the results returning exactly this query are obviously spam, but those returning the correct title should be the ones you'd download.
Also, if you cannot connect to Gnutella2, pick a hub on
this webcache, and see if it helps. As for eDonkey, you can update your server list with the following URL:
http://peerates.net/servers.php (Tools > Shareaza Settings > eDonkey > Download server list). Also, press F8, display the eDonkey server list, then click with the right button of your mouse on a server and then choose "Connect Now" and see if that helps to get you connected.