I just replaced the Display Housing and bottom case on my Macbook Pro... Didn't go so well. It was working before I started, and now its not. I haven't taken a second look yet to see what I might have messed up, but I will later on.
The top case is extremely easy, as the machine is built around the bottom case (assuming we're talking about the plastic model). The bottom case, on the other hand, requires you to gut the machine and rebuild it from the ground up. You'll have to pull the heatsinks off the processor, so have thermal paste handy. It's not an impossible job, but it requires a good static safe work area, a steady hand and attention to detail as there is some careful cable routing to do.
For the top case, Apple will do it for you if there are any cracks in it whatsoever, and this repair should be free.
So, I suggest that you go to the Apple store, have them replace the top, and then you would only need to buy the bottom case, and ifixit.com will help you out with that one.
Okay, i take back my earlier post. My Macbook Pro works now, and the repair, while tedious, was not that complicated. I bought my parts (Display with damaged LCD, New bottom case and new Optical Drive) all off ebay for $230 (that includes shipping). I wouldn't recommend doing anything if you still have your warranty though. The bottom case replacment involves taking EVERYTHING apart. It's not for sensitive stomachs, especially if it gives you any trouble when you try to turn it back on after the repair. I think the reason it wouldn't start back up right away was due to the PRAM reset after i disconnected the battery.
I've gotten parts from this guy and they are great. Good prices too. He may not have what you're looking for now, but he puts up new parts all the time.
I would use iFixit for the guide, but not for the parts. They have a higher parts markup than other vendors, I imagine to pay for the people who write the guides.
The top case is simple. The bottom case is a pain in the ass as you must disassemble the entire laptop in order to replace it.