Get a USB or Firewire enclosure for 2.5" SATA harddrives. Put the old drive in that and boot from it. Use SuperDuper! or Carbon Copy Cloner to clone your old drive to your new internal one.
As for replacing the hard drive itself, you can find full instructions on how to do it here.
It's a pretty simple and straightforward upgrade once you've had a good read through of the instructions, I've done it myself and it only took five minutes. Piece o' cake. 😉
I bought a new hard drive for my MacBook and took it apart (yes it is easy), but I have no idea how to take the pull tab/shield thingy off the old drive and put it on the new one. Looks like it uses torx screws perhaps?
Anyone know where to get a screwdriver like that, and what size to ask for? Apple doesn't seem to cover that in their instructions. I wish I knew that before I backed up everything and took everything apart. Now I'll have to reback up some things when I get the screwdriver.
Also the screws on the metal bracket that hold the RAM are weak. It seems like one is already getting stripped on the head and I only took it off twice (once to replace RAM).
I think I remember doing it with a really little flat head.. or maybe it was a sharp knife at the right angle. anyway, if you're delicate enough, steady and and use precise placement, there's no specific need for a torx set.. although it will make it easier 😛
-The Multi Purpose Kitchen Utensils Sales Man
Torx 7, IIRC. (maybe 6) Buy a little set at Sears or your local DIY store like Home Depot. Shouldn't be much in the cash department. I like the precision screwdriver sets from Sears.