How do I repair the top case of my MacBook?

"Topcase" usually refers to the surface of the computer which includes the keyboard, but from your description it sounds as if you are referring to the back of the screen casing. If so, unfortunately, no, that is not an easy piece to replace...it's actually one of the more difficult repairs you can do on this machine.

The back of the screen casing does not simply "pop" off as it would seem to, but rather it acts as sort of a tray that the screen, screen frame, and hinges are all screwed into. So it's necessary to take the screen assembly off the computer entirely, and then remove all the screen components from the back of the screen casing. Here's a hinge-removal guide that will get you most of the way there:

MacBook Core 2 Duo Left Clutch Hinge Replacement

If you're not feeling up to the repair (it's certainly one I am never too excited about doing), you might consider buying a cheap plastic cover for the back of the screen that would mask the damage. That is, if the damaged area does not prevent a cover from taking hold.

If you do take the repair on, you should be able to find the replacement part on eBay in the $20-$40 range. I wouldn't bother with superglue...in my opinion it would be a waste to do all the required work if you're not going to replace the part.

Good luck!