do this:
boot with your windows XP CD
goto recovery console (hit ‘r’)
type “fixmbr” then hit enter
then type “fixboot c:” then hit enter
restart your computer; it SHOULD boot right into windows XP
now in my computer, right click your d drive and format
put in your windows 7 disc, setup launches, choose “custom” installation (i think thats all you can do) and tell it to install on d drive, and install windows 7 like normal
when you are all done you should get a boot loader with 2 options: “Windows 7 Ultimate” and “Previous Version of Windows”
enjoy