Microsoft has erected its fourth PC store in a house.

Microsoft’s latest commercial features Cheryl, an American woman who doesn’t think she needs to update her 4-year old PC. Cheryl is the fourth individual to feature in part of Microsoft’s new Windows advertising campaign. The commercials are aimed at consumers who own previous versions of Windows. Microsoft previously kicked off the first round of commercials in early May.

Microsoft’s latest campaign coincides with a slowdown of PC sales. Market research firm IDC released its latest Worldwide Quarterly PC tracker results in April. IDC says global PC shipments declined 3.2% during the first quarter of 2011, compared to the same period last year. IDC originally forecast a 1.5% growth in shipments. “A spike in fuel and commodity prices and the disruptions in Japan added to the mix, further dampening a market struggling to maintain momentum,” says IDC.

However, as of today, over 20% of Internet-connected PCs worldwide are running Windows 7 according to Net Applications. It was an incredibly successful year for Windows 7 in 2010. Microsoft’s success with Windows 7 began before the product was even widely available. Released in October 2009, the operating system has received praise from consumers, businesses and the media. In November 2009, Windows 7 managed to surpass Apple’s Snow Leopard market share in just two weeks. In early February 2010 it was revealed that Windows 7 had reached 10% market share in just three months.

Windows 7 has also driven an uptake of 64-bit computing. According to ChangeBASE research, conducted with senior IT decision makers, more than 65% of businesses hoped to migrate to Windows 7 within 12 months of its release. Over 50% of those migrating will be choosing the 64-bit route. Microsoft confirmed in July that nearly half of all Windows 7 PCs run 64-bit versions. Forrester Research revealed in November that 1 in 10 PCs within North America and European companies are powered by Windows 7.

Windows 7 celebrated its first birthday after selling over 240 million licenses in the first year of sales. The company recently revealed it has now topped 350 million licences. Windows 7′s first Service Pack was made available in February and the company is currently working on SP2 and the next-generation version of Windows, codenamed Windows 8.