Hi Ajitabh,
As i told you earlier you can use temporary key also, for installation of Dashboard, but it is better to consult with SAP Sales team and get purchase SAP Dashboards 4.0 enterprise License.
For download temporary license key please refer below thread.
http://scn.sap.com/message/14291600#14291600
Below are the Temporary keys for Dashboards 4.0:
SAP Crystal Dashboard Design, Departmental Edition 2011
DB10E-N4VPB38-UXGDT9P-1A2XEH (Valid to September 23, 2013)
(also known as Xcelsius Enterprise 2011 & Dashboards 4.0)
Hope this will help you as well.
Thanks,
Daya