If you have an actual OEM info, just rename or delete the current 120X120 badge, copy the one that you like (must be 120X120px size), paste and rename it to the same name of the old file. The OEM info is located at: [Drive]:\Windows\System32\oobe\info e.g.: you may have an file named DELL_BADGE.Bmp, rename it to DELL_BADGE_old.bmp, paste a new one and rename it to DELL_BADGE.bmp It works too and you don't need to change the registry.
I think that you've installed DELL OEM DVD. So you can rename and replace it. How can you have DELL_BADGE.Bmp if you install Windows 7 from MSDN or TechNet ?????
Simple, I branded my computer with Hazar's tool and it installed all the logos at that folder. Do the same.