errrrr, the official answer... yes
The unofficial answer, no, you can use your upgrade cd to do a clean install of vista :)
to do this you have to install it twice though, the first time turning off all the automatic updates and not entering the product key, as it's not an update at this point the registration and the updates would fail.
Then as soon as it is finished installing start the install again and once again turn of the automatic update and don't enter the key(your not meant to upgrade vista to vista so they would fail again), but the second time it completes the install it will think it's done an upgrade and let you register it and turn the updates on and you have a clean install from your upgrade CD
Don't tell anyone I told you how to do this though :)
OH and make a note of this or print it of :)
Now don't anybody go using this info in the wrong way now!!