I installed a new HD in my MacBook just recently, and the way I did it was to pop the new one into a cheap USB enclosure (though you can get a nice FireWire/USB one if you plan on continuing to use it as an external, which is a good idea), then using Carbon Copy Cloner (google it, it's free) to transfer the contents of the old disk onto the new one, bootable and with permissions intact. Then you just swap the drives out, which takes all of two minutes in the MacBook (if you need those instructions, check Apple's site, it's pretty clear), and you'll boot right back up to the same pretty screen you had before. BTW, it's advisable, just to be safe, to go ahead and repair permissions after doing something like that, just in case, but they turned out not to need it on mine.
jW