I received your pm responses to my questions. You say you're using XP but you have no firewalls. Did you realise XP has its own firewall? Try configuring it as described here Firewall configuration instructions (click on link)

You said you have both Motorola Surfboard , Linksys. Can you possibly find out the model numbers of each one? This will be most helpful to know exactly how you're set up. I would imagine if there's any issues with these devices, it will be with the Motorola. Linksys uses UPnP & is generally very reliable to use UPnP (allows a program to communicate directly with the router to open whichever ports are required ... if the program is UPnP capable.)