Both Srini and Michael have provided some good information. I'd like to just add something. EiS will convert your discoverer reports to OBIEE through our conversion tool. As Michael said, it isn't an easy task but it can be done. We have a number of customers that have converted discoverer reports to the EiS eXpress solution as well as to OBIEE.
I'd be happy to put you in touch with the right folks at EiS to discuss how it might work for you. Please let me know if we can be of assistance!
EiS Solutions Director