Configure all your firewall to allow LW & Java to have access. Instructions here (Zonealarm link at bottom of page): http://www.limewire.com/english/content/firewalls.shtml
Update your Java: Java 1.4.2 (click on link)

If necesary: try by deleting LW's preferences folder called .limewire & found here: C:/Documents And Settings/your_username/.limewire

But only do it whilst LW is closed!!! But beware, once you've deleted them you'll need to reset all your option settings. So it might be an idea to make a record of these before you delete the LW prefs.