1. Go to Add/Remove programs in Control Panel and locate the NVIDIA block.
2. Remove the NVIDIA ForceWare Network Access Manager which uninstalls the firewall first of all.
3. Reboot, go back to Add/Remove Programs and choose to remove the NVIDIA drivers. From the menu that appears, choose the "Custom" option.
4. In the custom menu, checkmark the "Ethernet driver" field leaving the other options blank.
5. Reboot again and then go to C:\NVIDIA\nForceWin2KXP\x.xx\Ethernet\NAM (where "x.xx" represents the driver version you currently have installed) and run the "NetworkAccessManagerSetup.exe" file.
6. From the menu, checkmark the Ethernet driver field leaving the others blank. Once the driver installs, you'll be given the opportunity to install the firewall. Click "Yes" to that after which you'll have to reboot again.