finally am able to Upgrade my vCenter 5.0 to vCenter 5.1 with saperating SSO and Inventory services on diefferent and all other remaining vCenter services on other servers.
Thanks to Derek's great blog which helped to automate SSL certificate replcament with prestagin ssl certs.
http://www.derekseaman.com/2012/09/vmware-vcenter-51-installation-part-1.html