Why is upgrade from Windows XP® to Windows 7 not supported?
There are many changes in how PCs have been configured (applets, hardware support, driver model, and so on), and a clean installation yields the highest quality. The User State Migration Tool provides support for moving files and settings, but you must reinstall applications. For a set of customers this tradeoff may seem less than perfect, but the upfront time is well worth it. For more information about this topic, read the blog Engineering Windows 7: Delivering a quality upgrade experience. For more information about how to migrate data from Windows XP to Windows 7, see Step-by-Step: Windows 7 Upgrade and Migration.