Another nice thing about Vista are the games, they have a new game called "Ink Ball" which is pretty damn addicting
As far as installing Vista fresh, I know for a fact that both the upgrade and full version of Vista are identical, it's just the Windows key that determines which is an upgrade or full install in Microsoft's eyes.
I think that you could do a fresh install from the upgrade disk IF you have a previous version of Windows on the system before you install it.
I just bought the full version because I didn't know that there was an option to do a fresh install on the upgrade disk. I wish I knew that now.
You might want to check around to be sure, but my thinking is that they wouldn't have put the fresh install option on the upgrade disk if they didn't want you doing it.