Hi Tushar,
You need to discuss with the developer team regarding the portal upgrade.
After the upgrade,they have important role to play on the systems.
You need to have discussion on the below points
Points to be remember
1. Web Dynpro applications of NW 7.0 are source compatible to version 7.3 but not binary compatible and thus need to be manually migrated to the new platform.
This means that the old source code must be imported, re-compiled, and redeployed to the new system. In this scenario , you need to use NWDS which is compatible with SAP Netweaver 7.3
2. Portal applications developed with Java 1.4.2/J2EE 1.3 which is a default version of SAP NW 7.0 are generally source and binary compatible to those developed with Java EE 5 (JDK 5/6) in SAP NW 7.3 and thus do not need to be manually migrated
However for KMC-API and the UME-API it is necessary to adjust the source code before rebuilding and re-deploying the application.
3.In SAP EP 7.3,PAR files are not used Only EAR and WAR files are used to deploy.So we need to the PAR file to EAR file (Whcih is available in portal itself "Par Migration tool") and it can be deployed in the server
As per SAP, all those WD Java applications that were developed on NW 7.0 needs to be migrated on NW 7.3 if you plan to make further modifications.
Please do also follow the below links
http://scn.sap.com/docs/DOC-23061
For ESS/MSS
http://scn.sap.com/docs/DOC-41730
With Regards
Ashutosh Chaturvedi