"I received a new xps 8700 minitower with win 8 pro pre-installed. I believe this falls into dell's downgrade rules to win 7 pro." They are not "Dell's" downgrade rules ... they are Microsoft's downgrade rules, and yes, Windows 8 Pro (Pro ONLY) does qualify for downgrade rights.  Activation for downgrade rights is the responsibility of the user, so you can activate using ANY other license (even if used on another machine/account without affecting that license) ... a Dell installation DVD qualifies.  Normally, a Dell installation DVD does NOT require a key to be entered, and the range of systems that work with a DVD is extensive, but not universal, so if it asks for a product key, you will need to have one of your own to supply. Why do you want to downgrade?
I received a new xps 8700 minitower with win 8 pro pre-installed. I believe this falls into dell's downgrade rules to win 7 pro. The question is can I use a dell win 7 pro reinstallation disc from a dell laptop to perform this downgrade? 
Alternate way to downgrade from win 8 pro to win 7 pro