I had the same problem that Limewire wouldnt start when I click on the Icon. I checked in my Add/remove Programs box for the "old" Java 2 runtime Environment 1.2.1 or whatever but I didnt even find the 1.3.1 one. The only one that I had installed was the 1.3.0 one. So i gouess you just wanna make sure that you have the newest version installed (available at http://java.sun.com/Download5). It worked for me