Hi Simran,
with the API so far there is no defined way to post data, especially
using multipart post for binary data.
This isn't possible through the gadget API for type=html and the same
belongs to the opensocial API.
As Reinoud said you could use a new iframe, but that inhibits your
inner iframe from the
opensocial container, thus removes the ability to interact with the
container.
If this seperation of access is acceptable for your application, then
go on otherwise you should
rethink or redesign your application in order to fit into the
opensocial gadget API.
I hope that this will help you.