For original Macbook Core Duo and Core 2 Duo models, remove these 3 screws:

Two 3 mm Phillips near the right speaker.

One 6 mm Phillips threaded through a hole in a plastic finger above the subwoofer.

For Santa Rosa/Penryn and 2009 models, which don't have a c-channel:

Remove only the single 3 mm Phillips screw from the right speaker, and skip step 26.