The easiest way would two print servers connected to a router. I down like USB. I believe that it is a marginal port and usually results in conficts. IMHO.
I have 3 printers connected to 13 computer via a 3 port print server. 1 laser (Lexmark 4039 10plus), 1 dot matrix (for print labels), and one all-in-one (HP G85i). I use a JetDirect EX Plus3, 3 parralel port server. They make a USB verison for the new USB only priinters. It plug into a ethernet port on your router and is added onto your computer simila to a local printer.
I have not talked about multible printer on USB simply because I seem to have confict shortly after installing the secod printer. I have tried with little luck and great pain. If you have parralel printers you can install a second LPT port will little effort.
Just my opiinion.Reference