I've been running SmoothWall for over a decade. It is super simple to install and set up and is 10 times more secure than just the router. The cool part is it will run on just about any old left over computer you might have as it requires a Pentium200 and 128MB of RAM. It's a free download, all you'll need is an extra Networking Card.
http://www.smoothwall.orgpierre
