i bought a 7200rprm 160hdd mbp recently and i know i need an external drive. from what i've read, i should get a 7200rpm FW800 drive external drive. i'm just confused about what should be going on my external drive vs. my internal drive? put all of my raw clips on the external (HDV) and just grab clips to edit as i go? if so, where do the project files go as i move along in a video? i'm just not 100% clear on the definition of a 'scratch drive'. if anyone is using a mbp and an external hdd i'd love to hear your workflow/set-up. thanks.