You need a print server.
Basically you need to add your printer to the network, as most consumer printers only come with a USB connection you need a box that will allow you to plug your USB printer into an Ethernet port on your router, some will even work wirelessly.
One problem you may encounter is that some very cheap printers need various windows components in order to print, but most print servers have a tiny Linux OS onboard, so quite a few printers simply won't work when plugged in via a server.
Another issue is that most print servers (and there's not many different ones around) do not include two-way communication, so whilst they'll print fine, you won't get any status information like ink levels, paper jams etc.
I have a Belkin print server, but these aren't available any more, take a look at the Netgear PS121, which retails at £65 or the D-Link DP-G310 @ £85