The first AdSense Orientation Webinar took place on April 18th. It was an overview of AdSense for new publishers. Google is hosting a second orientation webinar tomorrow, Thursday, May 14, 2009 6:30pm (PST).
AdSensePro Obair said in a Google AdSense Help thread that this webinar will differ from the first in that Google would like to "spend more time chatting with you and answering your questions about this presentation."
You can view a recording of the first webinar below via YouTube:
You can register here for the new orientation webinar.
Forum discussion at Google AdSense Help.