Like the other poster above. I am not a big fan of upgrades. Better to do a clean instal, which does not mean you can't still use the upgrade version, if vista is like the past OS's. You will need an OS cd that has an upgrade path to Vista. You could borrow. Upgrades are usually cheaper too.
Just boot from the upgrade cd , on a freshly formated HD it will not find a previous OS so Vista will ask to see your old OS cd, for inspection. That is it.
My opinion is there are going to be 5 versions of Vista on one cd. If you do not have all the latest video cards / hardware...etc , you may have to settle for a watered down ver and xp may have been better, just a guess , still checking into this.