But it is true! We have about 20 not-for-resale copies of Windows Compute Cluster Server 2003 SP1. If you want one, please register as a community member on windowshpc.net and send a note to volker.will(at)microsoft.com. The license terms will allow you to install 1 head node and up to 10 compute nodes; You cannot resell the software, but it is otherwise fully functional.
If instead you'd like to try Windows HPC Server 2008, please register for the public beta on the Microsoft Connect site.