A year and a half after it first started selling Windows Vista, Microsoft is prepping a multi-million dollar ad campaign aimed at dispensing lingering doubts about the operating system. The campaign will tackle inaccuracies flaunted by Apple's infamous "I'm a Mac, I'm a PC" ad campaign as well as the widely publicized if under-educated opinions of online tech pundits.

The theme of the campaign is simple enough: Everything you've heard about Vista is wrong. And Microsoft has evidence to back up that claim, not the least of which is over 180 million licenses sold, a blockbuster number that, combined with recent PC sales figures, suggests new Vista users are coming onboard this year at a rate over 12 times faster than, say, are users of Apple's Mac OS X. And that was happening before Microsoft stopped selling Windows XP, so you can put that hand down now, Mr. Doubter.

But Vista's viability isn't tied to just sales numbers. After all, best selling products are frequently inferior to the competition. According to Microsoft, while "a few" users were disappointed by their early experiences with Windows Vista in early 2007, the company has made massive improvements to the OS since then. The Vista experience today, Microsoft says, is far superior.

The company highlights three areas of confusion.

Compatibility. Despite misguided reports and blog posts about Vista's compatibility issues, the truth is that Vista is hugely compatible with hardware and software today. The product supports nearly 77,000 hardware devices (double the number supported at launch) and runs 98 of the top 100 consumer software applications. Over 2700 applications are certified to run on Windows Vista.

Windows XP. Many have complained that Vista is just a prettier version of XP and doesn't offer much incentive to upgrade. Sure, XP is a great OS, and Microsoft says it's proud so many have embraced it. But the company points to Vista benefits like better security, faster and better searching, new and enhanced digital media tools (Windows Photo Gallery, Windows Media Center, Windows Movie Maker), new productivity tools (Windows Mobility Center, Windows Meeting Space, and Sync Center), integrated parental controls, pervasive PC and document backup functionality, hard disk encryption capabilities, and, yes, it's gorgeous new user interface as Vista-exclusive abilities that differentiate its latest OS from XP.

Performance. Despite reports that Vista is outperformed by XP on the same hardware, Microsoft can point to independent performance tests proving that Vista with Service Pack 1 (SP1) actually performs nearly identically to XP. In cases were XP continues to outperform Vista, Microsoft says that Vista is simply doing more on your behalf, securing your system against attack, indexing files for easier searching, and the like. But Vista also offers better power management functionality than does XP, a key concern these days. The notion here is that while the performance differences are negligible in day to day use, Vista's advantages more than make up for the difference.

While the actual ad campaign is still largely a mystery, here's what we know so far. Microsoft is spending about $300 million to promote its latest OS. It will focus on correcting widespread misconceptions with tag lines like "at one point, everyone thought the Earth was flat too" to put Vista's critics into the proper light. And it will be wide-reaching, with spots online and in more traditional advertising.

"We know a few of you were disappointed by your early encounter \[with Vista\]," Microsoft admits. "Printers didn't work. Games felt sluggish. You told us -- loudly at times -- that the latest Windows wasn't always living up to your high expectations for a Microsoft product ... Our goal is always to make each new version of Windows better than the last. With Windows Vista, we're convinced we succeeded."

So we'll soon see whether the world is ready to believe the truth about Windows Vista, or whether its competitors and critics will continue to control the conversation.