Microsoft has stepped up its effort to promote its Vista operating system, but Windows XP just isn't going away. The company reportedly extended the OEM downgrade timeline once again: As of now, system builders can still offer Windows XP downgrades to their customers and will be able to do so until Vista's second birthday.  Microsoft's deadline for allowing OEMs to sell PCs with systems that are 'downgraded' from Windows Vista to XP is still a moving target. Initially planned to expire on June 30 of this year, Microsoft at first granted an extension to July 31. However, OEMs are still selling the downgrade option (often for a premium) and, according to new reports, the deadline apparently has been officially extended for six more months to January 31, 2009. The information is based on one leaked email sent to an OEM. The decision indicates that there is still substantial demand for Windows XP and demand for Vista and its features may not be quite as convincing as the Microsoft usually claims. As before, the XP downgrade is available from some OEMs with the purchase a PC with Windows Vista Business or Windows Vista Ultimate.