Leopard’s built-in screen sharing is fantastic as long as you are going between Mac Leopard machines. For older Mac OS X versions, and for connecting to Windows machines, you’ll want to get Chicken of the VNC I know the name sounds cheesy, but this open source and free VNC client will allow you to view the screen of any machine that has a standard VNC server running, or even a Mac OS X Tiger machine with VNC functionality turned on.