We study how a server may disseminate a large volume of data to a set of clients in the shortest possible time. We first consider a cooperative scenario where clients are willing to upload data to each other and, under a simple bandwidth model, derive an optimal solution involving communication on a hypercube-like overlay network. We also study different randomized algorithms, and show that their performance is surprisingly good. We then consider non-cooperative scenarios based on the principle of barter, in which one client does not upload to another unless it receives data in return. A strict barter requirement increases the optimal completion time considerably compared to the cooperative case. We consider relaxations of the barter model in which an efficient solution is theoretically feasible, and show that obtaining a high-performance practical solution may require careful choices of overlay networks and data-transfer algorithms.