Install Retail Windows 7 Ultimate disk with Home Premium OEM CD Key

I have an OEM Windows 7 Home Premium cd key and a Windows 7 Ultimate Retail Install disk. What procedure would I have to do to install home premium with my cd key? Do I need to edit ei.cfg?

You will need to either edit the ei.cfg and replace Ultimate with HomePremium, or delete the file entirely.

http://windows7center.com/news/how-to-install-any-version-or-sku-of-windows-7/ gives a more detailed step-by-step process of doing so:

1. Open the disk image in 7-Zip
2. Delete or edit sources/ei.cfg:
   • Delete to have the option select the SKU you want during install, or
   • Change the EditionID value to be the SKU that you want:
     • Ultimate
     • Premium
     • HomePremium
     • HomeBasic
     • Starter
3. Save the image and burn it to disk