Mouse without borders.
TCP/IP Mouse/Keyboard sharing for Windows ...
"In a nutshell, it allows you to reach across your PC's as if they were part of one single desktop. I have two PCs on my desk at work connected to 3 LCD screens and using Mouse Without Borders I can move my mouse between the 3 screens, even though one of them is attached to a different PC from the other two. What’s more, I can move files between the 2 computers simply by dragging them from one desktop to another."
http://blogs.technet.com/b/next/arch...t-borders.aspx