Thanks for quick and valuable response, as you suggested I refer that document and register plug-in by following way
Use the old Windows vSphere Client to register a new plugin, through the Plug-in Manager view. Right click at the bottom of the list and select New plug-in..., then select the file containing the xml Extension data.
In this way I able to register my plug-in successfully as the old Windows vSphere Client display success message after registering new plug-in and I can also able to see the my new plug-in in Plug-in Manager view. When I start vigor server for my new vCenter web client and check server log I can see following message about my sample plug-in downloading in the log file without any error but I could not able to see my plug-in in web-client UI
[2013-02-26 15:25:59.562] INFO [INFO ] vc-service-pool-9 235BECDED30544746EE5C10E563DA639 com.vmware.vise.vim.extension.VcExtensionManager start writePackageToFile : com.acme.xyzPlugin.xyzPlugin
[2013-02-26 15:25:59.562] INFO [INFO ] vc-service-pool-9 235BECDED30544746EE5C10E563DA639 com.vmware.vise.vim.extension.VcExtensionManager Downloading plugin package from http://xx.xx.xxx.xxx:8080/examples/xyzPlugin.zip
[2013-02-26 15:26:00.234] INFO [INFO ] vc-service-pool-9 235BECDED30544746EE5C10E563DA639 com.vmware.vise.vim.extension.VcExtensionManager Done downloading plugin package from http://10.20.223.128:8080/examples/xyzPlugin.zip
[2013-02-26 15:26:00.234] INFO [INFO ] vc-service-pool-9 235BECDED30544746EE5C10E563DA639 com.vmware.vise.vim.extension.VcExtensionManager end writePackageToFile : com.acme.xyzPlugin.xyzPlugin
Please help me to short-out this issue