You need to check to see if your machine is running out of resources. A file that big needs to be loaded when the machine is "clean" ie: a fresh boot with nothing else running. I know I've loaded some _really_ big files, but can't say for sure they were over 600mb.
One way to import Dmoz, is to import it into 1.1x, then import that into 2.0
It's two steps, but it should work.
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