But can he be master of Microsoft’s domain? Jerry Seinfeld will play a key role in the software giant’s new $300 million advertising campaign, which is scheduled to launch Sept. 4, The Wall Street Journal reports. Seinfeld will appear with Microsoft chairman Bill Gates in ads and get about $10 million for the work. The new ad campaign, with a twist on the slogan “Windows, Not Walls,” is an effort to shake Microsoft’s stodgy image when compared to rival Apple Inc. Seinfeld has been a spokesman for American Express.