Its Simple. Only three steps. Every one says we cant install Windows XP over Windows Vista. Because Vista is the later version of Windows.
But Here i will tell you my own experience,
Step 1: For this step Remember you should have another fresh partition to install Windows XP. (Eg: In Drive "C" the Windows vista is installed. You should be having a new fresh partition to install Windows XP. imagine you have Drive "D")
Now Boot your system from Window XP CD/DVD.
Use the usual installation to install Windows XP.
Important: after the initial file copy, Windows XP reboots and loads up the GUI-based component of the install. You may get the following error: “A disk read error occurred – press Ctrl-Alt-Del to continue”. This is caused by a corrupt bootloader.
When the system reboots it won’t bring up a boot menu. Although XP recognizes the Vista partition it doesn’t recognize Vista itself. The Windows XP bootloader gets installed to the MBR and Vista can no longer boot.
(This Section can happen to you, some times not)When XP loads, open up Windows Explorer and you’ll see something interesting – a C: and (in this case) an E: drive. The C: drive contains Windows Vista, and as Windows XP can read NTFS partitions, it can browse and modify Vista’s file structure. More importantly, applications which have installation paths hard-coded into their install scripts rather than using Windows system parameter variables could easily dump files into C: when they should be installing to E:. This isn’t such a great situation.
Step 2: To restore Windows Vista Use the following steps. because you can’t use the Windows XP bootloader to boot Vista, we have to reinstate Vista’s bootloader to the MBR and configure it to manage both operating systems.
Boot from the Vista DVD and on the screen where you’re prompted to “Install now”, select “Repair your computer”.
The next screen searches for local Vista installations – there should only be one, so click Next.
This loads the System Recovery Options screen. Select the first option – Startup Repair. This looks for problems which would prevent Vista from loading (like a missing bootloader) and automatically fixes them.
If you click on “Click here for diagnostic and repair details” and scroll to the bottom of the list, it shows that the problem detected and repaired was a corrupt boot sector (according to Vista, anyway).
Click Close and then Finish, and the system will restart and boot into Vista.
Step 3: Boot Windows Vista and Install EasyBCP to enable dualbooting with Windows XP.
Click here to Download EasyBCP.
Launch the app and go to Add/Remove Entries.
Under “Add an Entry” and under the Windows tab and select in the Version drop-down list “Windows NT/2k/XP/2k3”.
Change the Drive (Drive which you installed Windows XP "Eg.E:\") to and the name to “Windows XP”, then click “Add Entry” and “Save”.
Reboot the system and you’ll have two entries in the Vista bootloader, and can boot into either operating system.
