Peer-to-Peer (P2P) networks are distributed systems where no central authority rules the behavior of the individual peers. These systems relay on the voluntary participation of the peers to help each other and reduce congestion at the data servers. BitTorrent is a popular file-sharing P2P application originally designed for non real-time data. Given the inherent characteristics of these systems, they have been considered to alleviate part of the traffic in conventional networks, particularly for streaming stored playback Video-on-Demand services. In this work, a window-based peer selection strategy for managed P2P networks is proposed. The basic idea is to select the downloader peers according to their progress in the file download process relative to the progress of the downloading peers. The aforementioned strategy is analyzed using both a fluid model and a Continuous Time Markov Chain. Also, abundance conditions in the system are identified.