These instructions are for physically replacing (upgrading) the hard drive in your Macbook. These instructions do not apply to Macbook Pros. Replacement/upgrade drives are available from several places, including www.mcetech.com. Macbooks are compatible with most 2.5 inch SATA hard drives and are commonly available in sizes up to 220 gb. 

Recommended tools: 
- #0 philips screwdriver 
- any small flathead screwdriver 
- T-8 torx hand driver or power screwdriver bit 

Macbook hard drives are located inside the battery bay, and are uncommonly easy to change for a macintosh. Get a #0 philips screwdriver (I recommend the precision long shank set Champion brand at sears, do not get craftsman, bad fit) and loosen the three screws on the chrome plate inside the battery bay. The screws are "captive" and will not come off the plate. Remove the plate and you'll see the two memory slots and a white tag. Pull out the white tag and pull on it and the HD will slide out in your hand. 

You'll need a T-8 torx screwdriver to remove the four posts on the old drive, and then take off the metal shield. Make a mental note as to whch side is "up" when you pull out the drive, that the connector end of the drive goes in first, and how far in the drive is pushed when installed. Don't remove the four posts on the old drive until you are ready to install the new drive. Be sure you put the metal plate on the correct side. Then just slide it back in, make sure it goes in all the way. Tuck the white tab back under the drive. 

When replacing the chrome plate, there is an ear on the short end that you need to it into the notch in the case first. The long end of the plate has two posts on it that fit in holes in the case, be sure those find their holes. There are two metal gaskets that will be caught between the plate and the case as you fit it in. I use a small flathead screwdriver to poke the gaskets in as I am closing the plate - you should not be able to see the gaskets at all when the plate is fully closed. 

Take care not to strip the screws when tightening the plate. Just turn them snug is fine. 

The drive will probably come from the manufacturer unformatted, and you will need to use Disk Utility (in the Utiltiies menu on the boot CD) to format it before you can use it. There are many choices for copying/migrating your information from your old hard drive to the new drive, which is beyond the scope of this post. If you can buy an external USB or firewire case (from the place you order the place you order your new hard drive from) to install the old hard drive into, this is strongly recommended and will make migration of your data much easier.