Ganesh,
i do not have an application handy which gives out base64. but this is so easy to setup, could you try setting it up and record a script? i can help you with any errors you may encounter with dfe's.
1.LoadRunner uses data format extensions (DFEs) to resolve the difficulties that arise from encoded data in Vuser scripts.
2. DFE support allows easier creation of Vuser scripts by providing the ability to decode the encoded data that is exchanged between the client and the server.
3. By providing the decoded format of the data, the information is presented in the Vuser script in a readable format that enables you to correlate and parameterize the script as required.
4. When the script is replayed, the DFE support re-encodes the modified Vuser script, and enables the Vuser to send the correctly encoded request to the server.
so yes. try to record a script. watch the traffic with a sniffer and see what it is