There are a variety of factors to consider here.

1. Your firewall. Are you using a router?? Have you configured it for the Gnutella network and have you password protected it?? On your XP setup you didn't enable file and printer sharing capablities did you?? Check your Windows firewall for access. Did you grant both TCP and UDP setting for LimeWire. Do you have any other firewall?? Check to see what other networks may be using your computer.

2. What other programs are you using that might be accessing the internet....antivirus, windows update, any other software updates.

3. shutdown internet access when you are finished and see what popup.