I found Synergy+! I have a Linux box set up next to my Windows one now, and I can slide my cursor between the monitors of the different machines, and control both with one keyboard and mouse! The Windows machine runs the server. I’m using a stereo Y-cable to connect both machines to the speakers. I’m concerned that it might not be good to connect two sound outputs to the same cable, although there are speakers so it’s not directly between outputs… I really need to learn about electricity!
Synergy+ was surprisingly easy to set up, and following the directions worked without issue. I set up sshd on the server using Cygwin by running ssh-host-config and following the instructions. Running ssh-keygen got me my RSA key for the client, which I copied into ~/.ssh/authorized_keys in Cygwin so that I could have passwordless login. With passwordless login, I was able to add the creation of an SSH tunnel alongside synergyc localhost. (localhost so that it uses the tunnel.) I also have the server running as a system service.
The end result is that Synergy+ is automatically started and securely tunneled. It’s pretty fun. Perhaps next in my string of projects will be setting the second monitor up on a monitor switch so that I can change between dual-monitor on one machine and one monitor each.
At the end of this break I will have attended no less than five Christmas parties. Too much travel!
EDIT: After accidentally closing Firefox on my left screen by attempting to open a menu on the far left of my right screen, I realized I could start the transfer range between screens at 5% and end it at 95%, making a part of the top and bottom of the shared edge not transfer. Hooray configuration!
EDIT Jan 17 2010: I now use autossh to make the tunnel persistent. Combined with Synergy+’s ability to retry connections, this makes it a lot easier to keep the machines connected between reboots.