I successfully installed windows xp on top of windows 7. My problem now is to boot Windows 7. I used the installation cd to repair the mbr. I used both the command-line and the gui to fix the mbr.
But here's what happened: The option to boot to windows 7 appeared. Together with the linux mint which I installed inside of 7(Wubi Installation). I booted with Linux Mint and it works fine. But when I tried to boot to Windows 7. The Starting windows boot animation appeared. But after 1-3 seconds a seemingly BSOD appeared. But it just appeared for about 1 second, then the system restarted. I have a backup of the mbr using easy bcd. What will I do? Did my little experiment failed? Do I have to reformat my system and do it over again? Please help, if you need more details, just ask in the comments. Thank you very much.
update I managed to boot to windows 7. I just changed the sata mode to ahci. My problem now is how to add xp to the choices of os to boot from. And will I still be able to boot to xp if sata mode is ahci? Do I have to switch the sata mode from ahci to ide everytime I try to boot to each of the os?