This is a plug for one of the handiest network programs I've used in a long time. Synergy.
In essence it's a software KVM. Only without the monitor part. You designate one machine to be the Synergy server. This is the machine that has the keyboard and mouse attached.
All other machines are Synergy clients. They have displays, but their keyboards and mice are tucked out of the way. Configure the server so that it knows where each display is (broadly, where are they in relation to each other, left or right?), fire up the server, and fire up all the clients.
Synergy then lets you sweep the mouse off the left edge of the server's display, and it appears on the right edge of whatever host you said was on the left. Keyboard input follows to whichever machine is currently hosting the mouse pointer. Synergy will also synchronise the clipboard as it does so, and can keep the screensavers of the different machines synced.
It's remarkably useful -- right now I have a (FreeBSD) server in the centre, with the Ultra 40 on the left, and a laptop in a docking station on the right. And I can literally "point" at the display that I want to work on, using just one keyboard and one mouse.
There's a Synergy website, and a Blastwave synergy package.