I did a little experiment yesterday and broke out my Sony VAIO for the first time in a long time. I downloaded Synergy on both my VAIO and Thinkpad and was able to synch them up so I could control both systems using my Thinkpad's keyboard and mouse. I connected a 24-inch monitor to each (the one on the left is my new HP monitor and the one on the right is my roommate's). Below is the resulting configuration.
And I thought double-monitors were cool!
As far as I can tell, there is no limitation to how many systems you can control from one keyboard and mouse using Synergy, and it works cross-platform with both Macs and PCs. (In other words you could use a Mac's keyboard to control your PC or vice-versa.) The only downside is that you can't drag windows from one computer system to the other, although you can cut and paste text between machines. (It also seems my mouse's scrollwheel doesn't work when I move the cursor onto the second computer.) The upside is that if I'm doing a processor intensive task on one machine, it doesn't affect the other in the slightest. Needless to say, I am quite impressed!
Here is a video to explain how it's done:
The best thing of all is that Synergy is free. It may take a little playing around with the software, but as the guy in the video says -- the results are well worth it.
P.S. -- Seems like this would be a great solution for using a laptop to control a computer hooked-up to a large screen TV from across the room.