Microsoft recently released the latest Windows HPC Server 2008

 Windows HPC Server 2008 (HPCS) combines the power of the Windows Server platform with rich, out-of-the-box functionality to help improve the productivity and reduce the complexity of your HPC environment.

Now, You can download the Windows HPC Server 2008 trial software and evaluate it free for 180 days.

Please visit the site:
http://www.microsoft.com/hpc/en/us/trial-software.aspx