Microsoft will make its bid for online advertising dominance with Engagement Mapping, a new ad measurement system which will be available in testing mode in March.

The software giant says it’s created a new way to determine the success of online ads. Engagement Mapping will look at all ways the was users are exposed to and interact with ads before making a purchase, rather than just the last site or search result they visited. The measurement system will take into account “the impact that recency, frequency, size and ad format (such as rich media and video) have on a consumers’ path to action,” the company says, but it isn’t offering any more details.

Microsoft and Google are already skirmishing over Microsoft’s $44.6 billion Yahoo takeover bid, and the ad effort is another attack on one of Google’s major strengths. Brian McAndrews, Microsoft’s senior vice president of advertising and publishing solutions, all but said as much in an interview with The New York Times last October: “Google gets all the credit, and in fact, you might have just gone to Google to type in the URL.”

Microsoft’s intention to enter the ad field became clear last May, when it acquired online ad company aQuantive (our coverage). The first Engagement Mapping results should be available at the end of the second quarter of 2008, Microsoft says. At that point, we’ll see whether Microsoft has much more to offer than the many other companies — including a number of start-ups — also developing ad measurement technology.