That is the question being asked at a thread in DigitaPoint Forums. An API or Application Protocol Interface allows easy access to data from third party application.
A post says, "I was told by MSN that it 'does not have an API option available', which I know is false, and I have found other information that says you must be a 'premium client' with certain billing requirements etc."
A MSDN Forums thread provides links to the adCenter API:
The following are the WSDLs used for the Microsoft adCenter API.
According to the Microsoft adCenter API Group: "We anticipate retiring the V2 WSDLs January 7, 2007, so plan your migration to the V3 WSDLs now!"