Well so far I have #1 results on MSN for work-in-progress sites which have very few pages and relatively few backlinks. From experience so far I'd say our #1 results on Google are mostly due to people linking to us with descriptive keywords, while MSN seems to leap at fairly high keyword density and keywords in <title>, <h1> etc.

So far I'd say it looks like MSN is very much influenced by on-page factors rather than link popularity.