I have successfully loaded suse 9.3 on one of two pcs at home [the one I'm using now is XPhome]. I have had the same thing now occur both with a sympatico connection and now a rogers connection here in Canada. [I just moved from NM where Comcast gave me no such problem]. I have the same Belkin router as then. The first time I plug into the network, linux sees the network and I am on my way - I loaded several updates. The second time, or the next day, the linux box is unable to see any site on the web - yet all conncections still give correct light signals that they are live. Neither Bell sympatico or Rogers supports linux but the latter suggested the router. What blows my mind is that it worked and then it doesn't with no changes.

Does your router act as a DHCP server?
You may find that on install the linux computer gets a IP from the router, and then due to some of your configuration then does not like recieving IPs any more, and wants to be static. That has caused problems for me in the past.
Try assigning yourself an IP within the range of your XP machine (as you know that works on the internet).