Do you have a 2nd computer for that, as well?

To clarify:

If you've got two computers, and only one screen, you can use a KVM, which is a piece of hardware which switches your keyboard, video output and mouse (hence the acronym) between the two computers.

Alternatively, you can use VNC or Remote Desktop (or X), which allows you to run programs (or an entire session) on the second computer, and have them displayed on the first.

If you've got two computers and two screens, you can either just use two keyboards and two mice, or you can use win2vnc or x2vnc or similar. They allow each computer to display on its own screen, but the keyboard and mouse are forwarded to the appropriate computer, meaning that you only need one keyboard and mouse.

If, on the other hand, you've got one computer and two screens, then just get another video card (or one with two outputs), plug both monitors into the same PC, and then extend your desktop across both screens (and on Windows, get a copy of Ultramon).

Or, you can do what I do: I have both screens plugged into the same PC, but I commonly have a Remote Desktop or VNC session to a second (or 3rd, 4th, 5th or 6th...) computer.