As you have already realised, the Starter Kit license key does not permit installation on a Windows 2000 Server machine. The software prerequisites listed on www.xmlstarterkit.com show Windows 2000 Professional, but not Server. But, hey, who has time to read all those boring prerequisites anyway!
Option 1. You install on a Windows 2000 Professional machine (but you already know that!).
Option 2. You contact your local Software AG office and arrange a test license. However, this means signing contracts, etc, etc, and only makes sense if you are planning a full-scale formal test of Tamino.
So, if you are simply wanting to get to know Tamino without any stress, you will need to find a machine using Windows 2000 Professional.
By the way, in case anyone else thinks otherwise, Tamino does run on Windows 2000 Server. The Starter Kit has simply been artificially restricted from doing so. It is a free test version of the software, after all, and is intended for personal use!
As a matter of interest, I wonder how many people out there have Windows 2000 Server on their personal machines. Maybe you are not the only one who has hit this problem!