If you have been dying to get into the MSN adCenter pilot program, Monday - March 6th is your opportunity. If you get in early, you will have already conquered any learning curve to the adCenter control panel, you will have the opportunity to get in while the CPC prices are still relatively low and you will be part of a small number of beta testers.
To sign up without requiring an invitation, Monday, March 6th after 12 (EST) (9am PST) go to http://adcenter.msn.com/ and more information will be there.
Forum discussion at WebmasterWorld and Search Engine Watch Forums.