MAKE YOUR WINDOWS XP PC AS A ROUTER

How to Make Windows XP PC as Router?
As an example, let say you have 7 computers and 2 network switches, and need to create 2 networks that can access Internet, so how to do it?? Some more information, one of the computers is equipped with 3 network cards and one of the network cards is connected to cable/DSL modem to access Internet, so this computer will act as a router!