I just checked and you have a Nat Firewall within your modem/router, so you will need to port forward....
This can be tricky, but take your time, read the instructions carefully and don't forget to do the static IP part...

One other thing, you only have to do a static IP for your computer once, after that you just open ports for whatever program you wish to use...ie your sons games...

These are your instructions for limewire...
Port Forwarding for the Motorola SBG 900

And the list for other programs...
PortForward.com - Free Help Setting up Your Router or Firewall

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