Overture (smart sons of guns that they are) frequently include "non-compete" arrangements so that other "primary & secondary" PPCs can not get in on the action. I think in eighteen to twenty-four months you're going to see an ad module for MSN but not an actual PPC. Don't forget about the pending lawsuit either - MSN is too smart to get involved with the likes of that.
I'm not sure a non-compete will be an issue. Keep in mind that MSN has it's own ad module based (very loosely) on PPC right now. You can go direct through MSN to get one of the top three spots. You just need big budget & a year commitment, and the system isn't automated in the same way we've grown accustomed to with OV and AdWords.
Beyond top three spots, they use Overture to fill the rest of the page, but don't do anything to mark the difference on the page. That probably gives them the backdoor they'd need.