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I'm not familiar with Desire2Learn at all. I had a quick look at their web site and there's not much of a clue except that they go on quite a bit about conforming to IMS standards. This isn't particularly good news as it is such a rambling standard that it would somewhere between difficult and impossible to support the whole standard. The result is that there are a couple of importers for specific implementations (e.g., Respondus and Blackboard 6).
Your options are really to first see if Desire2Learn can export to any other format that Moodle *does* support. After that I suspect you would need to think about funding the development of a suitable plugin.