Target disk mode. Connect the two computers with a firewire cable and then start up one of the machines whilst holding down CMD-T (the other should be started normally). The one started with the key combo held will be mounted on the other machine's desktop as if it were an external hard drive. Once you've transferred all of your files, just unmount the 'drive' in the usual way, disconnect the firewire cable and start up your other machine normally. Bingo.