Any computer bought after June 26th (but not before)with Vista Home or Ultimate is eligible. There is a form to fill out after the computer arrives: http://www.dell.com/content/topics/topic.aspx/global/products/landing/en/us/windows-7-consumer?c=us&l=en&s=dhs
If you bought a computer before June 26th, it is not eligible for free upgrade, but you can pre order it for $49.99. See the Windows 7 site for info.
The Dell site is showing an upgrade for certain laptops and desktops from Windows Vista to Windows 7 (when released) for free. After looking into the offer on a few sites, I can't help but ask if the deal is only for those select laptops or any laptop with Windows Vista bought after the "start date" (not sure what day it exactly was, but in any event, it has passed).
Could anyone offer some insight as to why this may be?