Microsoft is warning business customers that all support for Windows XP, still the most widely deployed PC operating system in corporate America more than a decade after it debuted, ends in two years. While that might seem like a ways off, the company said IT departments need to start upgrade planning now.

Microsoft also warned that support for Office 2003 also ends in two years--on April 8, 2014, to be exact. Additionally, mainstream support for Windows Vista ends Tuesday. That means the few Vista users that are out there will be charged on a per-incident basis for support going forward.

"If you still have some PCs running Windows XP and Office 2003, now would be a good time to start migrating them to Windows 7 and Office 2010," said Stella Chernyak, a marketing director in Microsoft's Windows group, in a blog post. "Windows XP and Office 2003 were great software releases in their time, but the technology environment has shifted. Technology continues to evolve and so do people's needs and expectations."

Despite the fact that it hit the market back in 2001, Windows XP remains the most popular desktop operating system in use today. Including both consumer and business environments, XP's share of the desktop market stands at just under 47%, compared to about 37.5% for Windows 7 and 7.7% for Vista, according to the most recent data from Net Applications.

The question facing IT departments still running Windows XP is whether to upgrade to Windows 7 immediately, or wait until Windows 8 debuts later this year. Chernyak said it makes more sense for enterprises to move to Windows 7 before Windows 8.

"We don't recommend waiting," she said. "Not only is it important for companies to complete deployment before support runs out, but they should also be aware that by upgrading to Windows 7 and Office 2010 today they can gain substantial results today while laying the foundation for future versions of these products."