All of you are probably aware that you can download MSDN Pre-Configured Virtual Machine Images and of configurations you can get with the VHD Test Drive. There is another option, though, if you want to evaluate a Windows 2003 R2 installation by itself on a virtual machine or as a host for Virtual Server 2005 R2. You can get a 180–day evaluation of Windows 2003 Server R2 at the trial software page over at Microsoft. This makes it easier to evaluate the performance of the server product, for virtualization, or for any other tasks that you may be considering it.
Link: Windows Server 2003 R2: How to Get Trial Software