My new laptop came with this: it means that the computer ships with Vista Business installed, and discs to allow you to install Windows XP Professional instead. The upshot is that you have replaced the shipped version with an older version of the operating system, hence downgraded as opposed to upgraded. It's exactly what I did on my laptop.
Although you have both versions of Windows, I believe that you have only one license, so you couldn't legally keep Vista on the machine you buy and also install XP on another machine.