A dual-screen hack - link an MS-Windows and X display

 This program merges the capabilities of x2x and vncviewer. It will allow a
 machine with an X display and a machine with a VNC server running on its main
 screen to act as if they were two displays connected to one machine. When you
 move your mouse pointer off the screen in a direction of your choosing, the
 pointer will appear on the other screen instead.