I just recycled an old (>8 years!) pc (Compaq deskpro EP 350 Mhz, 64MB ram) into a firewall using ipcop. It is rather easy to do, highly recommended. You can read about this here or here to make up your mind. I repeat, it is not that difficult, give it a try before generating more trash and old iron, and thanks to all the people involved in making ipcop! Did i forget to mention this stuff is free?