If you havnt got a new hard drive yet what you need is a 2.5" SATA hard drive. Anyone will do, its worth knowing this as you will probably get charged more for one with 'MacBook' specificity in the title.
Step 1: Taking out the Battery
Step 2: Getting to it
Step 4: Putting the hard drive in
Sorry for being sparing with the words but its fairly simple to do if you follow the pictures. Hope this was useful to someone :D