This paper presents the planning scheme for a cooperative agent-based multimedia retrieval architecture that integrates a heterogeneous set of repositories Into a coherent information system. The agents in the system collaborate In context of a conceptual query to formulate unique retrieval strategies for the different collections. The retrieval plan makes need-based use of Independent content analysis tools available on the network. The retrieval strategies for the repositories so formulated satisfy the specified constraints on quality of results and the response time requirements. The retrieval plan is reactively updated based on the retrieval performance at the Individual repositories. We present some experimental results to show the effectiveness of the planning scheme for repositories with different characteristics and the scalability of the architecture. We present a prototype implementation of this architecture that Integrates a set of dissimilar collections of multimedia data on Indian cultural heritage. A comparison of the retrieval results with some existing Internet search tools proves the effectiveness of the architecture.