Helping people with computers... one answer at a time.
There are two approaches to sharing a display, keyboard, and mouse with multiple computers. I'll give a brief overview of both.
I have two computers but only one monitor, keyboard, & mouse. I would like to set up a network (I have a router), but do I need any other software or hardware so that I can see & work on each computer without plugging & unplugging cables into each?
Not only are computers cheap and their displays often somewhat expensive, but there's only so much room on people's desks and in homes. Setting something up so that you can access more than one computer from a single station makes a lot of sense.
Given that I have perhaps half a dozen computers that I deal with from time to time here at home, this kind of set-up is more than just sensible - it's a requirement.
I'll discuss one common option, why I don't use it (though you might), and what I do instead.
KVM stands for keyboard, video, and mouse; this is a hardware device where you connect a single keyboard, display, and mouse to one side and two or more computers to the other. The computer connections are made through the keyboard, mouse, and video connectors (a USB connector is often part of the mix), so you may end up with three cables from each computer to this box.
Aside from the cabling, it's conceptually very simple. You connect everything up and simply press a button to switch from one computer to another.
The only real expense is the KVM switch itself and any additional cables that might be required.
I don't have a specific recommendation but a quick search at your favorite online retailer will show you many, many options.
Now, I have to be honest. While it's been a few years since I've tried to use them, my track record with KVM switches is abysmal. The ones that I tried rarely worked well; occasionally, they didn't work at all.
I use a different approach completely.
My approach is to take advantage of the fact that all of my computers sit on the same local network.
I simply enable Remote Desktop Protocol (RDP) on all of the Windows machines.
Using Remote Desktop, I can open a window that "is" the remote computer and drive it pretty much as if I were sitting in front of it.
In the screenshot above, you can see my desktop machine. The window in the center is the desktop of my laptop. I can then use my laptop simply by clicking on that window.
I have good news and bad news about this approach.
If you have the Pro edition or better of Windows XP, Windows Vista, or Windows 7, you already have remote desktop software on your machine and that machine can be remote-desktopped to (computers 2 and 3 in the diagram above).
Any version of Windows (and, in fact, Mac and Linux as well) can run Remote Desktop client software (computer #1 in the diagram).
There's no limit on the number of computers that you can connect to at once. I occasionally find myself with half a dozen Remote Desktop windows open to my other computers.
After they've been set up, the computers that you connect to don't even need to have a keyboard, mouse, or display connected.
It requires Windows networking to be set up properly, and networking is difficult to get right.
Once networked, running Remote Desktop is as simple as enabling Remote Desktop access on the computers that you want to connect to (typically, right-click My Computer, click Properties, click Remote), and running the Remote Desktop client on the machine that you want to physically use (typically, in All Programs, Accessories).
As I mentioned, Remote Desktop is available only if you want to connect to Windows editions Pro or better. If you have Home edition, Remote Desktop isn't an option.
VNC, however, is.
VNC stands for Virtual Network Computing and is conceptually the same kind of technology as Remote Desktop with a couple of differences:
Remote Desktop "takes over" the computer - only one person can use it at a time. VNC technology allows the computer to be used from the computer itself at the same time as it's being accessed by one or more VNC clients. All users see the same session - meaning that keystrokes and mouse movements may collide, but all can see and interact on the same desktop.
VNC requires that you install a VNC server on the machines that you want to connect to and use a VNC client to connect.
Besides having several of the same pros and cons as Remote Desktop, VNC has one more: it's typically available on Macs and Linux by default.
Here's my desktop again; this time with a VNC window open to my Mac laptop:
Ultimately, there are two paths to go. My recommendation is to avoid additional hardware and take advantage of your existing network and free software to enable remote access of any of the machines that you have networked together.