Hi Amit,
You can download the standard content from marketplace. Then all you need to do is create IDOC and Proxy configurations between ECC and PI and SNC and PI.
And then all you need to do is Integration Directory configuration that is all.
The details of configuration and message flow can be found here
http://help.sap.com/saphelp_scm70/helpdata/en/48/196210886e4e6fe10000000a42189c/content.htm
AND THIS IS THE SCENARIO YOU WANT
And you can readily find standard contents list on internet for SNC-- few links are here
http://help.sap.com/saphelp_snc70/helpdata/EN/57/6634418b718739e10000000a1550b0/frameset.htm
http://help.sap.com/SCENARIOS_BUS2008/helpdata/EN/48/8528b3ddfa3987e10000000a421937/content.htm
Regards,
Vikas