Centralized architectures based on the client server paradigm show their limits each time the Internet extends its capabilities. They present problems in terms of security, robustness, performance, high needs for administration. Short time solutions like load balancing and replication, or purchasing of more powerful hardware tend to cope with these limits for a while, but do not provide a definitive answer to these problems. Currently, different proprietary approaches hinder attempts to enabling communication between heterogeneous systems, while the Internet is developing toward a better interoperability with service-oriented architectures. Recent open source and standardization efforts allow building a framework providing an original answer to interoperability and scalability over the Internet. The use of Web Services (WS) as a means of communication between information systems, combined with a Peer-to-Peer (P2P) architecture for a more reliable network resources repartition and decentralization, forms a stable base for a new kind of distributed architecture. Furthermore, the composition and aggregation of multiple WS allow providers to supply with large scale meta-services. However, the use of heterogeneous WS in a dynamic context like P2P still faces challenges concerning the matching of WS and their respective interfaces. This paper discusses the use of mediation as an alternative to deal with the constant evolution of Web Services availability, and proposes a framework for a WS-enabled P2P platform.