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MSN gets its feeds from Ink, Looksmart, and Overture. So a listing in Overture or in Looksmart (including their Zeal directory) could get you into MSN. Also, Ink charges to crawl your site often, but they may have just found your site on their own during a crawl. Paying Ink is not likely to change your rank, just increase the frequency that they update your listing.
Jim
Let me expand slightly on a point that Jim made.
Some time this past summer (around August, as I recall) Ink made a major strategic change: they started spidering most of the web for free, just like Google does. Ever since I have been getting about 10% of my SE referrals from MSN, up from 0%.
I do not know how frequently they spider for free, those who pay get spidered every 48 hours.
I've noticed Inktomi repeatedly locating new pages on the site within 24-36 hours, when only one or two internal links to the page even exist.