http://synergy2.sourceforge.net/ lets you easily share a single mouse and keyboard between multiple computers with different operating systems. Synergy also merges the clipboards of all the systems into one.
In my setup a Windows Vista client is connected to an ubuntu server. I am using Scite on the Vista client. Unfortunately the Copy functionality is broken for me: It just does not seem to insert anything into the shared clipboard. Cut/Paste works. It also works with a local keyboard attached to the Vista client. Other programs like notepad do not show this behaviour.
I'm going to post this to the synergy bugtracker, too.