Yes, you can. Microsoft left a loophole in the Upgrade version of their product which works like this: 1. Boot to your DvD. 2. When asked for your Product Key do NOT enter it. It will ask you to verify that you're not inputting your Key. Again, tell it no. 3. Choose Custom Install. 4. Now do a clean install of Vista. 5. Once the clean install is complete and you're at your desktop for the first time run the install AGAIN from within Vista. This time, input your Product Key and choose the Upgrade install option. This takes a while, but it works great.