Recently, we have witnessed a tremendous growth of interests in streaming continuous media such as video data over the Internet. However, how to provide true on-demand streaming services with VCR functionality is still a challenging task, especially when their scalability is required. In this paper, we propose CoopStream, a novel streaming scheme, to address this challenge in the context of overlay networks. At the client side, we propose to use a dualchannel cache management mechanism to dynamically adjust the cache contents based on its current playing state, so as to support VCR operations locally. On the server side, we exploit the temporal relationship among asynchronous streaming requests to schedule streams. This enables us to reduce significantly the server load by redirecting streaming requests to the clients that can serve those requests. Simulation results show that, CoopStream is capable of providing continuous streaming services that are scalable in terms of the server bandwidth consumed.