Update: I bought a new Torx driver kit, and found that it actually IS a T6! I guess there are variations in how Torx screwdrivers fit into the nuts. Anyway, all seems good. My new 640GB drive is happy in its new home.

I got to this step, and to my dismay, I found that the Torx screws on the hard drive retaining bracket, and the new hard drive were NOT T6. The T6 screwdriver just goes around and around in them. Anyone else have this problem, and know the correct size? It was quite a bummer, since I had to reassemble the whole thing without having completed the project.