clone your 80gb you have in there at the moment to an external if you have one, then use migration assistant to copy your user back onto the new hard drive and everything should be the same as before
i didn't have this option before and i just burned a bunch of blank dvds and cds and transfered everything over that way but I would say it is worth it to get an external or at least an enclosure to swap drives in because the cd/dvd way is a PITA to reorganize everything and reinstall everything