I would like to: Video cable from desktop, to laptop, & use the laptop video to monitor the desktop, & would a KVM switch allow usage of keyboard & mouse?
No. It won't work. Laptops don't have any video "input" ports. You can use a KVM switch for keyboard and mouse only to use one keyboard and one mouse on both the PC and laptop. But you cannot use the "V" (video) side of that again, because there are no video "input" ports on laptops. Laptops only support a video out to display the laptops video onto an external monitor or briefing projector.
Bill are you familiar with 'VNC' at vnc.com. No cables to connect, just install the viewer on the machine you would normally use, install 'server' on the other machines. FREE! I've connected 4 pc's using VNC works fantastic!
Yeah, it has been around for years. Of course, you still need a network connection. There are many remote apps like this - including Remote Desktop Connection built into many versions of Windows.