I have replaced drives in these models a number of times. It is not that hard. You don't have to do a teardown or anything. You just have to remove the keyboard. There are just a lot of screws, and you have to be careful with the keyboard ribbon cable.

Make sure you are on at least 10.6.8, and don't forget to install Trim Enabler. (For 10.6.8 you need version 2.2).

http://www.groths.org/software/trimenabler/