whs, it is certainly confusing. There is a section in the installation guide (last link, above) that talks about a clean install when: "You want to install Windows Vista on a separate partition of your hard disk, and you have an operating system on your computer and an available partition." I would think that you could do the same if you leave the hard drive with Vista on it in the system. The upgrade installer will see that you have Vista, by looking at the hard drive, and should allow you to install Windows 7 to the SSD. However, I would also expect that it would somehow prevent Vista from running when it's done.
At the bottom of all of these MS support pages is a link to "Contact Us" which talks about how to reach MS support by phone, e-mail, and chat. If you change the location from United States to Germany, I would expect the Contact Us link to give the appropriate phone numbers.