Microsoft confirmed Tuesday that it will sell upgrades for Windows 7 to users running the Windows XP operating system. Those users, however will have to do a "clean" installation of Windows 7, meaning that all data on the machine will be lost. "Regarding XP, customers can purchase upgrade media and an upgrade license to move from Windows XP to Windows 7," a company spokeswoman said Tuesday morning. "However, they will need to do a clean installation of Windows 7."  In a follow-up reply to questions, the spokeswoman fleshed out what Microsoft means by upgrade. "The 'upgrade' part is referring to the license," she said. "You will be able to get the discounted 'upgrade' license, but it will include full bits." Although Microsoft Tuesday spelled the six planned versions of Windows 7, it declined to provide pricing for them, or for the XP upgrade licenses. Typically, an operating system upgrade offers users the choice between an in-place migration of the machine -- including installed applications and all data -- and a fresh installation, which overwrites the hard drive's contents. When Microsoft launched Windows Vista in January 2007, for example, it offered people then running XP those upgrade paths.