As of July 1st, Yahoo! Sponsored Search (Overture) ads will no longer appear on MSN or Windows Live. They have been slowly phasing the ads out anyway but tomorrow is the official end to the agreement between the two companies. Now if you want PPC exposure on MSN, you'll have to us Microsoft's AdCenter itself.

Official announcement From Yahoo!:

U.S. Sponsored Search Listings No Longer on MSN

MSN's U.S. search distribution agreement with Yahoo! Search Marketing ends this month, and Yahoo! Sponsored Search listings will no longer appear in MSN's U.S. search results. Although we regret the loss of MSN as a distribution partner, it was not unexpected, and we do not anticipate a significant change in the total amount of traffic to our advertisers as a result.

We expect that MSN will continue to display Yahoo! Search Marketing Content Match listings in the U.S., and Sponsored Search listings in non-U.S. markets, beyond June 2006