Hoping you guys can me with a web access problem.

Since upgrading my PC to the latest XP SP2 version, I am not able to view web pages though my netgear FM114P.

Some facts which may help solve the problem:

1. I can view web pages by plugging my PC direct into the cable modem (allows me to write this post!).
2. I have tried spoofing the router MAC address to match my PC, but this hasnt worked.
3. With the FM114P connected, I am able to ping my tivo within the internal network from my PC, and I can ping external IP addresses.
4. I cannot access tivoweb from my PC through the router (on the internal network). I am prompted for a username/password, but am not served with the tivoweb home page.
5. I have just grabbed all the Windows updates, but no luck

Any help would be much appreciated. Ditching Windows XP is probably the correct solution, although this is not an option for me at present.