iMacKid hit the nail on the head. And all laptop drives made since probably 2000 or 2001 are 9.5mm height.

I do have one thing to add, though. The same thing I add to all laptop hd upgrade threads; if it fits in your budget, consider getting a 7200rpm drive. They have no effect on battery life to speak of, they are no louder or hotter (excluding Toshiba, which makes garbage drives anyhow) than their 5400rpm counterparts, and there is a significant performance benefit to be had by going with a 7.2k drive.