Hi Charlie
Look on
this thread and
this post
If you have a Vista License, you are entitled to using an Upgrade version of Windows 7. Yuo will have to do a clean install, you are not allowed to do an in-place upgrade from Business to Home Premium (unless you want to
tweak your installation files or
your registry, which I don't recommend, a clean istall is a better way to go anyway)

Let me know if you need additional info