It's safe to assume the DIVX player isn't the problem.
If you can't change your IP address, it's definitely your box.
Ok, when you run winipcfg, on the top drop down box where it lists your adapter, when you are verifying your IP is changed, did you select the belkin card out of the list to view its config? Often times, by default winipcfg picks a PPP adapter for config viewing.
My recommendation to you is this...
1. DUMP the USB NIC you're using for internet access if your cable modem has an RJ45.
2. Go buy a wired router. Best Buy has them for $20 after rebate.
3. connect broadband to router on WAN, connect PC and DIVX player to the router.
4. Exclude the IP address the DIVX player is set to from the IP range under DHCP settings.
5. Keep your PC set to auto config for IP.
Advantages:
1. You don't need to put up with the confusion of a multi-homed (multiple NIC) computer.
2. Win98's net code stack constantly screws up when you try to get a little freaky with it, such as, you guessed it, multi-homed NIC configs. You eliminated that problem.
3. Better online security.
4. Better system performance due to not using a USB NIC, and not having two network cards running.
5. You can easily share your net connection now if you need to.
MCSE, MCSA Messaging, baby!