1. Make sure you're using Java 1.5 & not Java 1.4.2;
Setting up Java 1.5
2. Have you seen
QuickTime 7.0.4 bug stops LimeWire from opening!
3. If the 2 computers are networked, make sure your router has UPnP enabled. If it doesn't have UPnP ability then port forwarding may be required.