Google, meanwhile, is also eyeing DoubleClick's market. The search giant plans to roll out a competing service that lets users place ads on sites beyond the search giant's own network in the next few months, the Journal quoted sources as saying.

But the ensuing brawl between Google and Microsoft could end up damaging investors in Yahoo!, too. As Google continues to dominate text-based search, to the Redmond, Wash., software giant's dismay, Microsoft may be angling for another way to participate in the booming online ad market by going after rich [video-related] display advertising instead.

And DoubleClick, a player in the display market with its huge roster of relationships with online publishers and its blue-chip list of clients, could give it an entry point.

"It would be a good start from Microsoft's perspective because it would give it a much broader reach for rich media and a way to get more into the business," says Ani Kortikar, the CEO of search marketing firm Netramind. "And if you're Microsoft, you don't only want to go after Google in text advertising, which is [Google's] strong point."