The blogging world is buzzing about the discovery that you CAN perform a "clean" installation of Windows Vista from an Upgrade version!
- Boot Windows Vista Upgrade DVD
- Click "Install Now"
- Do not enter Product Key, which installs the 30-day trial
- Select the Windows Vista "upgrade" version you actually purchased
- Complete Windows Vista installation
- When Windows Vista launches, reinsert the Windows Vista Upgrade DVD and launch setup.
- Perform an in-place upgrade
- NOW enter your Product Key
OPINION: In the future Microsoft will reconcile all Windows Vista Upgrade serial numbers not associated with a Windows XP serial number during the Vista upgrade process. My advice? Don’t do it . . .
The Road to Know Where 
Your advice is probably good but…. I suspect a lot of people who want to perform a clean install with Vista actually previously had XP and therefore have an XP serial number, so what do you think are the chances that MS will let them supply that serial number without having to go through the insanity of installing XP merely to immediately upgrade it to Vista? The reason I ask is that I attempted to upgrade my existing XP and after the install hung 3 times I guessed (incorrectly as it turned out) that the hang was caused by XP so I wiped the machine and did a clean install (it took another 5 attempts before it actually completed). I am now at step 5 and was very happy that I would be able to enter my legitimate Vista upgrade serial number using step 6 (especially as there is no other way I know of that works). With your opinion however, I just don’t know…