Why go upgrade and Ultimate when you can go full install OEM for system builders for less seen on the Home Premium edition?
Microsoft Vista Operating System 66I-00715 Home Premium on DVD for OEM Computers Only 1 Pack-Best Computer Online Store Houston Buy Discount Prices Texas-Directron.com
For the higher price the Ultimate edition offers 4 things different then Home Premium namely 3 features for networking and one hardware protection feature. When going to install to replace 2000 that will take the Windows, MyDocuments, and Programs folders and put them into a Windows/old folder for retrieving files later.
The problem with an upgrade disk is once 2000 is gone you would need to reinstall that version or another if you have to reinstall Vista for some reason later. The price seen there is the best seen so far for saving on price too.