I have recently been playing with the Synergy software, which allows a single mouse and keyboard to control multiple computers whatever operating system they may be using. I am currently using my PC's mouse and keyboard to write this on my macbook pro!
It's pretty easy to set up, the windows server is pretty simple, the only bit the documentation does not emphasise enough is that the screens must be named after the hostname of the computer, so for widows it's the 'Computer name' and for OSX/linux it's the output of the 'hostname' command. The linux and OSX client is command line only which is quite annoying but otherwise a very nice piece of software.
Oh and it's free!