1. Be sure VISTA firewall is disabled if using Norton Firewall. They two will clash otherwise and will cause problems. Also, be careful with Norton. If you do system or norton or LW updates, you may need to reconfigure LW for norton. ie: remove previous firewall rule and re-add.

2. If still problems, it may be your router. In that case, port forward it.
First step is the most important & must be done correctly else the process won't work: (a) Setting up static ip for VISTA
(b) follow directions here Port Forwarding for the Motorola SBG 900