I could successfully call the deployed webservice_producer(on ubuntu) from a vb application(on win XP Prof.). Now I'd like to extend my application to exchange more complex data between the vb application and the ESB.
1) What should be the structure of the data to be exchanged? message.xsd?
2) Any idea on how to realize this?
Well it really depends on what your requirements are and what you mean by things like "more complex data".
In terms of exchanging data between your VB client and an ESB endpoint... webservices, file drop, raw HTTP, FTP, email...