Searching search.msn.com for "linux" will really highlight the weakness of MSN's search features -- the results are actually supplied by three different companies, then stitched together.
MSN provides up to five "featured" sites for a search phrase, usually to companies that have marketing relationships with MSN (like Amazon or eBay).
Overture gets to throw three "sponsored" sites at the top of every page of results, so these are companies who bid to be shown for a particular search term.
LookSmart provides the "directory" results. Of course, you get into the LookSmart directory by paying a fee to have your URL(s) associated with certain (a) certain search phrase(s). In the case of a search for "linux", you have to wade through 400+ directory results before you get to...
"Web" results, which are provided by Inktomi. Inktomi's engine collects URLs in one of two ways: through a regular crawl of the Web (like any search engine), and through a fee-based "paid inclusion" program where companies can submit their sites through a direct XML feed into the Inktomi index.
At least, that's the way it works for now. Given that both Inktomi and Overture have been bought by Yahoo!, there's very little chance that Microsoft wants MSN to fatten a competitor's coffers. Microsoft's moving as fast as they can to get their own technology in shape to replace the outside vendors. But MSN Search isn't powered by Microsoft quite yet.