go to amazon and look for the western digital 320gb passport
i bought 3 of these, replaced my macbook pro's 120 with it, my moms macbook 80gb with it, and my dads hdd.
its a good idea to get an external hard drive since you can clone your hdd straight onto it and then swap it with the one inside your macbook with no probs at all. after you replace your old one with the new one, you can easilly put the old hd into the external set up and then snap it back into the case to use again later as an external drive. this passport can easilly be open then reassembled