Hi! Here's the part:
For some reason there doesn't seem to be an iFixit guide for this, so here's the best web tutorial I've seen related to taking apart the screen enclosure:
Please note, it's geared toward replacing the screen, but the iSight is right above the screen and is pretty self-explanatory once you're in there looking at the dissected screen frame.
Also keep in mind, the iSight itself is only one link in the chain, and the cabling connecting it to the board could also be at fault. However, replacing that cable involves opening up the hinge, which is not fun, so I'd probably go with trying to replace the iSight itself first, and then proceed from there.
Another note, if possible you might want to wipe your system and reload, just in case a bizarre software issue is causing the camera to not be recognized. Now that I'm thinking about it my girlfriend's iSight was not recognized, and when I wiped it and installed Snow Leopard, it was for some reason usable again.