Hi Naseem,
Integration Gateway is a new component of SMP3 which allows you to connect to different back ends like SOAP, JDBC,JPA, fetch data at runtime and convert it into OData models to expose data as an OData service.
You can find lots of documents available at SCN. I.e.
Integration Gateway: http://scn.sap.com/docs/doc-50022
SAP Netweaver gateway has been renamed as " SAP Gateway" is a set of ABAP add-ons to existing SAP ERP system.
For more information check:
http://scn.sap.com/community/gateway
(Look at announcement at the same page)
To respond to your question:
"sap Integration Gateway" is not same as "sap gateway".
Rgrds,
JK