How to dual boot when Windows XP was installed after Windows 7?

It seems pretty straightforward to dual boot those versions of Windows when the newest is installed after Windows XP. But the inverse isn't happening on my machine. I tried even editing the BOOT.INI file, but the boot just freezes or displays that a file is missing when I try to boot another partition.

Currently I'm stuck with Windows XP, and I need to boot my Windows 7 instead.

What is the solution?

You need to reinstall the boot manager. NTLDR can't boot Windows 7.

Start the Windows 7 install DVD, and choose "Repair" and "Command Prompt". At the prompt, do a "bootrec /RebuildBCD" to write down a new bootloader.

I can't promise that this is going to keep Windows XP in the boot order, but it will restore the ability to boot Windows 7. After that, you can follow any number of articles to get Windows XP back into the boot manager manifest.

This should help you out: Install Windows XP in Dual Boot with Pre-Installed Windows 7