Microsoft has hired comedian Jerry Seinfeld to anchor a $300 million advertising campaign designed to burnish the image of its struggling Windows Vista franchise, according to The Wall Street Journal.

The newspaper, citing sources familiar with the arrangement, reported Thursday that Seinfeld will be paid $10 million for the work and that the campaign will launch on Sept. 4. The campaign was created by the Crispin, Porter + Bogusky agency of Miami.

Microsoft officials were not immediately available for comment.

The software maker is desperate to counter widely popular Apple ads that personify Vista as a bumbling, middle-manager type while portraying Apple's Leopard OS as a cool hipster.

The ads, which have become part of popular culture, have helped boost Leopard sales and may be partly responsible for the widely held perception that Windows Vista is cumbersome and hard to use. Few businesses have upgraded to Vista from Windows XP, citing concerns about Vista's cost, compatibility with older software and intrusive security features.

Microsoft's dominance of the computer operating system market has declined significantly in recent years as viable alternatives to Windows emerge.

In addition to Leopard, the open source Linux OS is going mainstream as distributors such as Ubuntu add features designed to make it more user-friendly. Wal-Mart earlier this year began selling Everex's Linux-based gPC for less than $200.

It's all taking a toll on Windows' market share.

In 2007, only about 39% of new computers shipped with Vista on board, compared with the 67% of the new computer market captured by Windows XP in its first full year of availability in 2002, according to data from Microsoft and Gartner.