I don't see any UPnP options from the models I saw at PortForward.com - Free Help Setting up Your Router or Firewall so perhaps port forwarding is the way to go for you. If it doesn't support UPnP or it's unreliable then PF is definitely the way to go. Go to that link & find your CompUSa model or similar. First & most important step is always setting up a static ip: PortForward.com - Setting up Static ip then follow other directions given. Hope it works ok.

Oh & don't forget to configure your XP firewall to allow LW full access: Firewall configuration instructions (click on link)