I haven't had the chance to use it yet, but I've been anxiously awaiting an Adwords Editor type tool for MSN. It's still in beta at this point, but if anyone's used it I would love to get your feedback. It looks like it has the potential to drastically improve the MSN experience. Their interface, though much improved in the past year, is still clunky in spots when compared to Google.
The post below contains more info and a form where you can sign up for the beta test:
Announcing the adCenter Desktop Beta - adCenter Blog for Advertisers