Connecting two computers to one screen

There are some solutions to this:

A control mechanism that lets two or more computers share a single peripheral, such as a printer, a scanner, or a monitor. With an A-B box in use, the user can decide which computer is able to use the device at any one time by turning a switch.

Here are a few devices:

http://www.nextag.com/vga-monitor-a-b-switch/search-html

If you want to connect more than one computer to the same monitor, look for a monitor with multiple inputs and an easy way to switch between them.

http://products.howstuffworks.com/computer-monitors-buying-guide.htm

If you want to save a bit more space,  use a KVM switch - you'll be able to use one screen, one keyboard and one mouse with both computers. I won't cost a lot.

You can use a KVM switch as it has already been pointed out, and that will also allow you to use the same Keyboard and mouse. I currently use one. They work great. Found it at pcclub for under $30 using the PS2 connection, be careful to make sure you get the right connections for the mouse and keyboards if you intend to use this. It will allow you to use one adapter one on one mouse on one side. So if you have USB get a USB KVM save yourself the hassle.