Hard Drive Replacement help

Left my powerbook burn a dvd last night and woke to a horrible grinding noise.. which i'm guessing means the hard drive has died....its about 2 years old now... what I wanted to find out is what hard is good to buy to replace it with?? is it 2.5in? Has anyone else replaced their hard drives...any problems??

Also another thing..when i've installed the new drive..will simply rebooting with the OS10.4 disc in be enough to reinstall tiger? or do i need to do any keyboard combo when booting up?

Many thanks!