XP Professional and Home are divided into two general product categories for Microsoft, namely business and consumer products. XP Professional, as a business product, will receive mainstream support for two additional years after the release of Windows Vista (whenever that may be). After that, Professional will have an additional five years of extended service (minimum), though this could be lengthened considerably if the OS update after Windows Vista does not ship within three years of Vista's debut.
Based on the current timeline and our own expectations for the launch of Windows Vista, we estimate Windows XP Professional Mainstream Support ending in late December 2008, with Extended Support ending in December of 2013. It could stretch out longer, but we don't expect the window to be more than two to three additional years. After the Extended Support phase is finished, online support (knowledge base, FAQ, etc.) will continue for 10 years.