I have an Windows XP box with 2 NICs, one which connects to the Internet, and the other connects to a network router over Ethernet. I have other pcs which are connected to that router, and I want them to be able to connect to the Internet.
1. Set static IP details for the NIC (the one that connects to the router).
IP address: 192.168.<x>.1
2. Configure the router's WAN settings.
Router's IP address: 192.168.<x>.10
Be sure to check that your LAN and WAN are on different subnets. For example, if your router is at 192.168.10.10, it should give out addresses in the range, say, 192.168.20.100-199.
This is because some routers don't allow the LAN to be on the same subnet as the WAN (mine didn't); even if yours allows this, you should still use different subnets as a precaution against collisions.
3. Edit the registry value of IPEnableRouter to 1:
You could have hooked everything up to your Router and allowed it to do all the work for you. Now you have to keep that PC on in order for other computers to have internet access.
The purpose of a router is to connect to the internet. If DHCP is enabled in the router, all computers would need to hook up to the router. If you have a WAP in place, you would simply need to configure that with a static IP address and make the Gateway the IP address of the router. Problem solved.