Mizz Matrix

Here is the link that will lead you to the port forwarding instructions for your modem/router, this should solve your problem:

Port Forwarding for the Linksys WRT54G


UK Bob

PS. You will need a different "Port Forwarding" configuration for each P2P app you use, the one above is for LW, but as you know your modem can store these configurations quite safely.

PPS. If you still can't connect then ask your ISP if they have started to "Bandwidth Shape" your Internet connection.