Okay, I have replaced my internal hard drive before on the same macbook I am using now.
What you need to do is when you put the new one in, you need to also put in the Mac OSX install disk, once that is done, hold in the 'option' button when starting up, select the CD. then install mac on the new hard drive (just follow the on screen instructions when the cd boots up). once thats done, you will be able to start up from your new hard drive!!! Put all your information back on it, if you want too. Then you're finished. remove the cd and enjoy your new hard drive
HOPE I HELPED!!!!!
What you need to do is when you put the new one in, you need to also put in the Mac OSX install disk, once that is done, hold in the 'option' button when starting up, select the CD. then install mac on the new hard drive (just follow the on screen instructions when the cd boots up). once thats done, you will be able to start up from your new hard drive!!! Put all your information back on it, if you want too. Then you're finished. remove the cd and enjoy your new hard drive

HOPE I HELPED!!!!!