Currently in the US MSN displays Overture, Looksmart & Inktomi results.
When Overture results are diplayed they are shown on top, but they are only shown for some searches (I think it's somewhere around 30k phrases they're used for)
Looksmart will be replaced at the end of the year, but they are still currently being listed under "Web Directory Sites" (in the US). MSN runs their own algo over Looksmarts database to rank the listings (The title/description that looksmart gives you plays a major role).
Inktomi results are currently displayed last ("Web Pages"), Although they should be getting a promotion in Jan..