Microsoft Corp. is scheduled to stop selling its Windows XP operating system to retailers and major computer makers Monday, despite protests from a slice of PC users who don't want to be forced into using XP's successor, Vista. Once computers loaded with XP have been cleared from the inventory of PC makers such as Dell Inc. and Hewlett-Packard Co., consumers who can't live without the old operating system on their new machine will have to buy Vista Ultimate or Vista Business and then legally "downgrade" to XP. Microsoft will still allow smaller mom-and-pop PC builder shops to buy XP for resale through the end of January. A version of XP will also remain available for ultra-low-cost PCs such as the Asus Eee PC. A group of vocal computer users who rallied around a "Save XP" petition posted on the industry news site InfoWorld had been clamoring for Microsoft to keep selling XP until its next operating system, Windows 7, is available. The software maker has said it expects to release Windows 7 sometime in 2009. Last week, Microsoft said it would provide full technical support for six-year-old Windows XP through 2009, and limited support through 2014.