I actually had to figure this out for myself recently, and i got it switched out, but now I refer to it as my Fugly external, cuz it don't go back together nice.
I'll describe this as if i'm taking a book apart as that seems the easiest analogy. The first step was to remove the stiff rubber from what would be the part near the "spine" of the book. I then put a small screwdriver between the "cover" and the "pages" and worked it around popping apart little plastic fasteners that run the entire length of the drive. if you've ever opened an ipod it is similar.
Once you've got the two parts popped apart, then you can pull the "cover" off the pages by sliding the "pages" directly away from the "spine." At this point you should be looking at the guts attached to the "pages" frame, and the cover can be set aside. Now, getting the drive out will involve popping off the sata and power connectors, and then you'll have to grab a screw driver and start dismantling the internals.
Once you get the old drive out just reverse the process. It won't look pretty at the end, these things aren't designed to be opened up, but it will work just fine.
however, you follow the above instructions at your own risk.
