I think after reading the title of the article, one thing might be striking your mind i.e. whenever I install Windows XP over Windows vista/7, previous OS get lost and I able to operate windows XP only. Now, I will provide you with the simplest solution over this problem.
Firstly, you are having windows vista/7 in your system, if you are going to install windows XP, make a partition empty for installing windows, with the help of Disk Management Application
After completing the above task, now insert the bootable CD of Windows XP and restart your system and boot it with CD. After the completion of installation of windows XP, your system will get automatically restarted and you might be wondering where is your previous operating system Don’t Panic!, it was not present there because of the misplaced path(Boot File’s Path) of previous operation system.
Keep Going with windows XP and after configuring the windows XP, now install this software DualbootPro in your windows i.e. in windows XP. This software will allow you to make entries and changes to the boot record. This software is useful for Dual booting Windows XP, Vista and also for the latest Windows 7.
Now with the help of this software you can Add New OS Entry, and other options will help you getting your previous operating system back!!!
Have you got your OS Back? Facing any Problem? Do let us know.