Also, I'm pretty sure Apple won't do it, but you can get an Apple authorized rep to do it for around $100 + cost of the drive I think. But if its a Unibody MBP then just do it yourself... If it's a Classic and you are somewhat tech savvy, then do it yourself, its not that hard.
Which computer do you have (or interested in changing HDD). The Unibody MBP is very easy to change. The older MBP is a bit more difficult to do but its not that hard. I did it with the help of the guide from ifixit. I suggest that you go and look up the guide for whichever model of mac that you own and see if you ould do it yourself. Whatever you decide, good luck. If you do decide to do it yourself make sure that you have the right tools.