There is a lot of confusion around Windows XP support and migration with SCCM 2012.  Here is a good article on how to migrate user data from Windows XP to Windows 8.1 with System Center 2012 R2 Configuration Manager.

http://blogs.technet.com/b/configmgrteam/archive/2013/09/12/how-to-migrate-user-data-from-win-xp-to-win-8-1-with-system-center-2012-r2-configmgr.aspx