Win2VNC is an excellent utility that brings in other monitors to your desktop. Normal vnc brings the desktop of your remote machine into a window on your local desktop. Win2VNC keeps the monitor on the remote machine and sends your mouse and keyboard to the other screen. So you get more screen real estate and still only need one mouse and keyboard. Thanks to Chris for mentioning the unix version of this
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this tool doesn’t like a dual headed system. If you try to control a dual head the main monitor switches off. If you control FROM a dual head then the secondary monitor can not have the mouse moved to it. Actually on further testing it gets really confused. Sometimes you end up on the second machine but can’t get back to the second monitor, othertimes you can’t get into the second machine. It normally works the first time you go off the edge of the screen but fails if you come out and go back in again (if that makes sense)