A cheap and easy way of adding a router to your network is to use a surplus PC with Windows XP Professional installed on it. Just install an additional network card in the box and then configure the registry setting below and Presto! Your XP box becomes able to route (forward) IP packets from one interface to another.
Open Regedit and navigate to:
Find the following registry value:
Set this value to 1 to enable IP routing on the box.
After doing this, reboot the machine. You may also need to disable Windows Firewall on the machine.