The solution is Synergy. It’s free open source software from http://synergy2.sourceforge.net/. One computer will have to serve as the server, the rest will be the clients. It works on Windows, Mac, or Linux. On Macs it’s easiest to set up Synergy with the SynergyKM Preference Pane, http://software.landryhetu.com/synergy/. I haven’t tried it but there’s another Mac client at http://www.altuit.com/webs/altuit2/SynergyOSX/Instructions.htm. The instructions there will help you get going. Once you’ve got the Synergy server running on one machine, you can run the client on all the rest. The machines must be on the same network segment and Synergy must be permitted in your firewall settings.