The laptop works, right?
If the laptop is broken, then it might not be possible to do what you want. Obviously, if the display is broken then it's a non-starter.
If the laptop works, then you can use it as a second monitor in a number of ways. The method I use is synergy
Synergy is a cross-platform program which lets you control multiple computers from a single keyboard/mouse. You set up your main computer as the synergy server, and you set up the other computers as synergy clients. The mouse/keyboard of the synergy server can control all of the other computers. You simply move the cursor off the edge of one screen to enter another screen. It's like a multi-monitor setup, except each of the monitors is actually a different computer.
On the laptop, you can open up an xterm and ssh into your main computer. Thus, the laptop doesn't really do anything other than accept remote keyboard/mouse input, and displaying a terminal interface ssh'd into your main computer.
You can also run remote X applications in any of several ways. However, if you mainly just want a terminal display, then running an xterm and ssh'ing into your main computer is the most efficient solution. Note that synergy will forward the clipboard. You can cut/copy on one computer and then paste on another computer.
Synergy is a wonderful alternative to multi-head, especially if you have laptops and/or you need to use multiple operating systems.