New
#31
I have reread the thread and can't find where you confirm that you are booting from the DVD and using Custom>Advanced drive tools to delete XP, create New partition(s), then format using Windows 7 formatting which is different than XP.
Other than that if I had a DVD that worked before but won't work now, I would give it a good cleaning.
Where did you get the original DVD? Did you burn it yourself? Try reburning it with Imgburn at 4x speed with verify.