More on PCs not getting to the Internet

We have a home network with 2 PCs. Lately, when one PC is on the internet, the other cannot get on and vice versa. What could be happening? Both our PCs are running XP. The Cable runs to the router, which runs to the hub, which we both hook into. If one PC wants to get on the internet it has to restart to do so thus knocking the other off. We have road runner and they have basically said its a problem with the hub. I called the manufacturer of the hub and they say its a problem with road runner. I am running in circles–please help.