You can use a firewire cable to boot one of the macs into target disk mode.
Doing this makes one laptop appear as an external HD on the other mac.
Connect them both with a male to male firewire cable turn ONE mac on then when its is fully booted hold down 'T' on the other mac while starting it up. Once its booted it will appear on the desktop of the first mac and you can navigate as you would an other HD.
Im not sure how 'migration assistant' works so cannot comment on it or what cable is required. Beinf from Apple though I can assure you it will be a breeze to use.
During the initial set up of your new MacBook, at some point it will ask if you want to import settings from another machine. From there, Migration Assistant will walk you through everything. As everyone else has mentioned, just make sure you have a firewire cable ready.
anybody know if i can do this with a firewire 800 to 400 cable? i need to transfer files from my Powerbook to my MacbookPro and i only have a Firewire 800 and a Firewire 800 to 400 cable, they came with my external hdd. Cheers!