Need help moving from Windows Vista to Windows 8, here are the details....

So I have a Windows Vista machine that I built 5 years ago in college. I used a Windows license that was given to me free from the university however I do not have any physical media with Vista on it (we had to return the discs after installation.)

Ok, now here is my problem, I just ordered all the parts for a new PC from Newegg and would like to run Windows 8 on it when it comes out in the fall. I want to use my current Vista license to get the discounted Windows 8 price.

How do I get Windows 8 (at the discount price) onto my new hard drive using my Vista license that is activated on my old computer?