I've hooked up WD MyBook to the Edge with no problem...of course that one has external power. So it's likely that the power is the issue.

Of course, I don't know why you need that much disk space when carrying the Edge around...I was only hooking it up to an external hard drive to move recordings and PDFs and porn and such out of my Edge's precious onboard memory, so it's not like I'm carrying the drive around with my Edge all the time.