Xp home upgrade disk wil not let me reinstall

I have a xp upgrade disk that was provided by the retailer when I purchased the machine. After inserting the disk in cd rom, and booting from disk, I am given the typical windows intallation screen. however, when i select a new installation, I am advised that the windows version on the computer is newer than the one I am trying to upgrade with. I already no this as sp3 has been installed on the machine. I still want to do the reinstall as there is a multitude of problems in the currently installed os. how can i get past this message?