Just when you thought there was no place left on your PC for advertisers to hock their goods, Microsoft is now allowing businesses to sponsor your Windows 7 desktop images. And you know what, it's kind of cool, at least compared to the maddening intrusiveness of ads on Web sites and in instant messaging programs.Slideshow: Windows 7 in Pictures: The Coolest New HardwareA Windows "theme" is a package that includes desktop background images, a screen saver, a window border color and a sound scheme. Some themes include desktop icons and mouse pointers. One of the desktop images in the Porsche Windows 7 Theme.The brands in the ad-sponsored Windows 7 Themes for your desktop are mostly hidden. You won't be seeing a giant Coca-Cola logo draped across your desktop, but rather a collection of weird and wacky images from Coke's "Happiness Factory" ad campaign with a Coke bottle placed in the background. The Porsche and Ferrari themes deliver lustrous images of their sports cars. It's pure eye candy for car lovers.The ad-sponsored themes are part of a pilot program that Microsoft is calling the Windows Theme Experience and can be downloaded by Windows 7 users at Microsoft's Windows Personalization Gallery site. [ For complete coverage on Microsoft's new Windows 7 operating system -- including hands-on reviews, video tutorials and advice on enterprise rollouts -- see CIO.com's Windows 7 Bible. ]The themes are available to Windows 7 users only if they want them. Microsoft is stressing that the ad-sponsored themes are opt-in, and will not be forced upon users.The program will run on Windows 7 until Oct. 2010 and currently includes advertisers such as Coca-Cola, Ducati motorcycles, Infiniti, Porsche, Pepsi, Ferrari and Twentieth Century Fox. Microsoft itself is also participating, with themes for Bing and Zune.I don't like to feel like I'm being tricked into peddling products. But I got over that and downloaded a few Windows 7 Themes. The Bing theme offers stunning photos from exotic locations (though the "Bing" logo in the lower right is a distraction). The Pepsi "Refresh Everything" images simply repeat everything and are lame. The Coca-Cola "Happiness Factory" images are much more fun, and the Porsche car images are a thing of beauty. If I can't buy a Porsche, at least I can gaze at their best wheels on my desktop.What do you think of branded desktop themes in Windows 7? Offensive or cool? Any brands you'd like to see included?Shane O'Neill is a senior writer at CIO.com. Follow him on Twitter at twitter.com\/smoneill. Follow everything from CIO.com on Twitter at twitter.com\/CIOonline.