First of all, uninstall both ZA & LW (start > all programs > LW > use the uninstall option there, don't uninstall LW from control panel).

Now reinstall LW & make sure to use the offline installer (when you click to download, cancel the dialog box which pops up & now use the option to download the offline installer).

Once LW's installed, reinstall ZA & make sure that the Windows firewall really is turned off. That's been a fix for some Vista users.

What happens when you do this test http://www3.limewire.com:6346/ ?
Is this your first try with LW?

If reinstalling ZA doesn't help, check out the threads below. The first one's a really old post but a few people have recently found that it's solved their problem
For those who can't connect

If that doesn't help, there are other fixes to try in the thread below. Just remember to have LW properly closed before replacing gnutella.net file & deleting preferences folder. Also, when replacing Java versions, remember to have only 1 version of Java installed at a time.
If LW Will Not Connect