To get the Messenger buddy list of a user, try looking into the Contacts Control. You cannot (as far as I know) strip all addresses from it (also known as "scraping"), but you can make your application interact with it.
Danny Thorpe has an excellent blog detailing what you can do with it (and often how, as well).
It's the best thing next to writing an application to log in to the Messenger servers directly (which is not allowed, and its unrecommended).
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