Social computing and online communities are changing the fundamental way people communicate and share information. Social computing focuses on how users may have more autonomy to express their ideas and participate in social exchanges in various ways, one of which may be Peer-to-Peer (P2P) file sharing. Given the risk of opportunistic behavior by malicious and/or criminal communities within the P2P networks, it is crucial to understand the factors that affect individual's usage of P2P sharing software. In this paper, we develop and empirically test a research model which includes trust beliefs and perceived risks as two major antecedent beliefs to the usage intention. Six trust antecedents are assessed including knowledge-based trust, cognitive trust, and both organizational and peer-network factors of institutional trust. Our preliminary results show general support for the model, and offer some important implications for software vendors in P2P sharing industry and regulatory bodies.