Originally posted by: Matthias99
Get another switch or hub, plug into one of the ports of your router. If your new switch/hub has an "uplink" port, use that with a straight-through cable to connect. Otherwise hook one of the regular ports of the switch up to your router with a crossover cable. You can continue doing this (chaining more switches and hubs together) more or less indefinitely to add a large number of systems to your network.
Very easy upgrade.