Windows Vista : Whats the difference between Windows vista and windows vista upgrade?

ok, i looked at vista boxes, and i saw 2 different windows vista ultimate. I saw Windows vista Ultimate cost around 500$ and Windows vista Upgrade cost 200$. What the hell is the difference?

Should be the same at the end of teh day once installed, asit says UPGRADE ie you MUST have Xp to get the upgrade or it wont work!

Not sure if M$ Win 2000 will go Vista on theupGrade the box will tell you thou

Or you pay full price

jiuk