I'm certain you couldn't grab just any webcam and install it, but I'm sure it's possible to find one if the particular laptop in question came with one. Just realize most of the time the cable for the webcam is integrated into the LCD cable. You might need to get a new LCD cable, or just replace the whole screen assembly.
--- side note ---
Most webcams are probably just USB. It might be possible to rig something up. Say, if you have the cable, run the line through the LCD, into the laptop, and solder directly to one of your USB ports (loosing it's functionality, of course). It's definitely not going to be any easy task, and I doubt it'd work.