Vista
hey,
here is the whole deal with Vista. If you want to buy and install Vista, they actually give you one DVD with all of the different versions on it. For instance, if you purchase the bottom of the line "Vista Windows Starter 2007" and then you want to upgrade to "Windows Vista Business", you simple purchase an upgrade and Microsoft give you a new key to unlock the upgrade features on the DVD. Basically, all 6 versions are on the DVD and the key you purchase enables you to an "express" upgrade.
Here are the version names last time I checked, could have changed though.
Windows Starter 2007; Windows Vista Enterprise; Windows Vista Home Basic, Windows Vista Home Premium, Windows Vista ultimate, and Windows Vista Business.