I will soon be traveling with my D700. I would like to be able to download images from the flashcards. I have a card reader. The question is, what should I download images to. I do not want to depend on carrying around a laptop. I thought I might buy one of the stand-alone external hard drives I see advertised for around $100. Then, I plug the card reader into the hard drive and download away. My question is, what powers the external hard drive? Will it run off the camera's power supply or do these things have external power cords? In general, how do these external hard drives work, exactly? What should look for in such a unit? What are reliable brands of these things?