Posting to confirm that Western Digital's one ter drive DOES fit in the late 2009 13in uMB. I tried to take pictures of the size difference but it wasn't really visible. If your still a sceptic, open it up and you'll clearly see the drive is 3mm smaller than the cavity. It fits a 12.5mm like a glove. The WD10TPVT from Western Digital is the drive I'm using. There are various guides all over the internet, including Apple's own DIY replacement guide. Here's a readers digest of them all, oriented for technical, non-handholding users. Tools needed: Phillips #0 screwdriver, Torx T6 Recommended: Back up with Time Machine. If you have a 250GB internal, a 250GB external will work fine, and last I knew they were $60 at Walmart. 1. Remove all 8 screws from the bottom. Slide your fingernails under the bottom near the fan exhaust and pop up. There are three latches, one dead center and one on each side halfway down. These just pop out. 2. The black bar above the hard drive, the "retaining bar" must be removed. Two captive screws and it pops out. 3. Pull the hard drive out by the sticky tab thing. Unplug the SATA cable, and stick the tab on the new drive. There's enough sticky for it to stick. 4. Remove the four T6 screws (retaining studs) from the old drive and place them on the new drive. These are the only thing holding the drive from bouncing up and down in it's cavity. This isn't required though, because a 12.5mm drive fills the whole cavity, but it's probably a good idea. I didn't have a T6 handy. 5. Plug the SATA cable into the new drive and put it in the cavity. 6. Drop the retaining bar back in and screw down the two screws. 7. Snap the case back together and screw it down good. Those screws don't like to go in straight. Recommended: Stick in your Snow Leopard install DVD and from the utilities menu, click Restore from Time Machine Backup, attach your external, and watch it grind away. The process would be the same for Leopard I imagine, but I wouldn't know.