The 'force IP' option doesn't exist in later LW versions.

First of all, make sure that your XP firewall's configured to allow LW.
Firewall setup

Then you could try port forwarding for your router. The instructions are here.
Port Forwarding for the Alcatel SpeedTouch 536v6
Don't forget the step of setting up a static IP address. LW's listening port, port in the 'manual port forward' box & port forwarded within a router must all be the same number