If you're running a couple Linux boxes with a monitor on each beside each other, you gotta try this. I'm using this program called Synergy2
http://synergy2.sourceforge.net. This is sharing a mouse/keyboard with two machines. The two machines I have running are a Mandrake 9.1 box as server and a Slackware 9.0 box as client. This program is cross-platform, so if you have a Win box or a Sparc machine, it should be good to go (I know it works with Win98se as client). If you're running tightvnc or whatever you might like x2vnc. I've read about it, but never used it.
http://freshmeat.net/projects/x2vnc/?topic_id=55,. The setup for Synergy2 is simple and easy to follow. I've been running this for a little more than a week now, and I love it. Using NFS, pulling files back and forth with this little program is sweet. The only thing is, you have to be logged into X for this to work as either server or client. Check it out.