Sept. 18 (Bloomberg) -- Microsoft Corp., the world's largest software maker, will start a new phase of a $300 million adverting campaign today without spokesman Jerry Seinfeld.

New commercials will feature celebrities such as actress Eva Longoria and rapper Pharrell Williams, spokesman Frank Shaw said. The ads, developed by the agency Crispin, Porter & Bogusky, are part of Microsoft's biggest campaign ever.

The Seinfeld commercials debuted Sept. 4, depicting quirky conversations between the comedian and Microsoft Chairman Bill Gates. The first spot showed Seinfeld and Gates shopping at a discount shoe store. A second had Gates and Seinfeld moving in with a stereotypical American family. Neither commercial mentioned Microsoft's flagship Windows software.

``They've gotten all they could from ads about nothing and now may be moving on to ads that say something,'' said Rob Helm, director of research at Directions on Microsoft in Kirkland, Washington. ``They wanted people to pay attention to its campaign, and this was a way to do that quickly. Now they will try to deliver an actual message.''

Microsoft always intended to switch gears for the ad campaign's second phase, Shaw said. ``It was completely in accordance with the plan,'' he said.

A call to Seinfeld's office after business hours yesterday wasn't immediately returned.

Vista Difficulties

Early customer complaints about Vista, the newest version of the Windows operating system, hurt the brand, as did Apple Inc.'s Mac-versus-PC television spots, which poke fun at Windows. While Windows sales fell short of some analysts' estimates in the quarter that ended in March, they rebounded the following period.

In addition to using humor, the ad campaign is intended to publicize improvements to personal computers and the retail experience, Brad Brooks, vice president for Windows consumer product marketing, said earlier this month.

The company realized it needed to connect with consumers using ``a light touch,'' Brooks said of the Seinfeld-Gates pairing. Microsoft also needs to run a continuous campaign to stay involved with customers all the time, he said.

Microsoft, based in Redmond, Washington, rose 18 cents to $24.75 at 9:41 a.m. New York time in Nasdaq Stock Market trading. The shares had dropped 31 percent this year before today.

To contact the reporters on this story: Connie Guglielmo in San Francisco at cguglielmo1@bloomberg.net; Dina Bass in Seattle at dbass2@bloomberg.net

Last Updated: September 18, 2008 09:43 EDT