How do i dual boot windows 7 and xp

i had 7 install on my had drive then i added a second hard drive and installed xp to the second hard drive. i can boot into both seperatly if i change the primary hard drive to the one i would like to boot to. how can i make the windows 7 hard drive the primarry and still me able to dual boot with windows xp added to the start up boot loader i tried doing this using vistabootpro but have had no luck it will make the windows xp item display but when selected it will restart my whole computer i can also see each hard drive in my computer on both os's i have also tried using cmd to confgure the mbr to load xp didnt work it said all processes were completed succesfully but the werent i also ran it as an administrator just to be safe i would like to do this without formatting my hard drives at all because i have data that i do not wish to backup and restore please help me with this asap
-Blaine Miller