While Yahoo! Search Marketing and Microsoft Advertising adCenter are similar in a lot of ways, adCenter treats ad copy length and keyword mapping in ways that require some changes as part of the your transition. Making these changes will help smooth your transition and get your ads live in adCenter as quickly as possible.
Here's a quick list of 3 important tasks to complete in your account: Shorten ad titles and descriptions, Expand your keyword lists, and Check your bids. Read the details in the PDF embedded below or on Yahoo blog post (linked under):
More Info: Preparing for the Transition to adCenter