With your Mbox, you're going to setup your sessions on the the external drive and leave them there. You won't ever want to move them to the internal drive, nor will you have to because running of the external drive will work great.
I will recommend Lacie drive soley because that's the only external drive I use on an everyday basis, and I think they work great. I'm sure there are better out there, but I am very confident that Lacie just works. Feel free to research it and find a better, or even take suggestions from other people, but we have about 10 of their drive in the studio I work at, and we rarely have problems.
Your iBook has a 6 pin connection, and this will work fine with a Lacie drive.
Oh yeah, don't get a Lacie Porsche drive. Those blow. Just get a D2, or something similar.