Hi
Kind of, what I was suggesting was to physically move the hard drive to a hard drive enclosure not just copy the info. This way you can also use your old drive as a handy external hard drive once everything is done. This would involve purchasing the enclosure first obviously if you don't already have one.
The migration assistant will run automatically if you do a fresh install of Tiger or Leopard on the NEW hard drive once you have installed it in the powerbook. Then simply connect the enclosure containing the OLD drive and you're ready to migrate, it's really simple to use and does all of the work for you. It can also be run afterwards from /Applications/Utilities/Migration Assistant.app.
If you don't have the enclosure and want to get one you're looking for an enclosure for a 2.5" ide drive, they're not expensive.
I would also suggest looking for the service manual for the powerbook if it's your first time opening it up - it's not difficult but you can never be too careful
Hope this helps