Install Windows XP on Your Pre-Installed Windows Vista Computer
Continuation...
Now we'll change the CD drive to use E: by selecting that in the drop-down.
Now we can create a new partition for XP to live on and make sure that the drive letter is set the way we want. If you do not create a partition now the XP install will do so automatically, but it's easier and cleaner to do it this way.
Right-click on the Unallocated free space area and then select New Simple Volume from the menu.
Follow through the wizard and select whatever options you'd like, making sure to use D: as the drive letter.
Now you will need to close out of disk management and reboot your computer. This is because we can't do the next step until we reboot. (you can try, but it won't work)
So we've come back from rebooting… open up Computer from the start menu and then right-click on the D: drive and select properties. Give your partition a meaningful name like "XP". It would be wise to name the C: drive to "Vista" at this point as well.
Now you'll want to pop your XP cd into the drive and boot off it. You may have to configure your BIOS to enable booting off the CD drive, or if your computer says something like "Hit Esc for boot menu" you might want to use that.
Once you come to the screen where you can choose the partition to install on, then choose either the unpartitioned space or the new partition you created. Whatever you do, don't try and install onto your Vista partition! See how much cleaner it is now that we've labeled each partition distinctly?
We'll assume XP is completely installed at this point, and you will have lost your ability to boot into Windows Vista, so we'll need to use the VistaBootPro utility to restore the Vista boot loader.
To Be Continue.....