how do you reseat the rubber hard drive guide on a Macbook?

My daughter's MacBook hard drive crashed. I was told that there was a dried spot on the metal case that covers the bottom of the hard drive, so the warranty was invalidated. They gave me back the MacBook with the hard drive removed. When I went to put in a new one, the rubber guide on the side of the rail was partly out of place. I cannot get a drive to seat completely, as the rubber rail bunches. How do you reseat the rubber rail? I saw a link in another Apple Discussion that pointed to a forum in Canada. The person there said he had to open the case to reseat the rubber rail. If that is the only way to reseat the rubber, how do you open the case? I have taken apart Thinkpad's so hopefully working on a MacBook will not be too difficult. Thank you.