Structured P2P systems have been developed for constructing applications at internet scale in cooperative environments and exhibit a number of desirable features such as scalability and self-maintenance. We argue that such systems when augmented with well defined consistency semantics provide an attractive building block for many large scale data processing applications in cluster environments. Towards this end, we study the problem of providing transactional semantics to P-Ring a P2P system which supports efficient range queries. We first extend a commonly used replication protocol in P2P systems to provide well defined guarantees in the presence of concurrent updates and under well defined failure assumptions. A multi-version concurrency control protocol called LSTP which leverages the guarantees of the replication protocol to provide transactional semantics is proposed. LSTP is designed to provide useful consistency semantics over P-Ring for read intensive workloads without sacrificing the scalability and other desirable properties inherent to the system. Under LSTP, read-only transactions are abort-free and non-blocking and the index stores no state for such transactions. We show that LSTP ensures no missed dependencies between transactions and guarantees basic consistency for read-only transactions when update transactions are serializable. The design of LSTP and its provable properties is a proof of concept that P2P systems can be augmented with transactional semantics. Results from a preliminary simulation study are also presented.