Desktop Grids utilize computational resources of desktop computers in their idle time. The BOINC middleware for organizing Desktop Grids has an architecture developed to unite a large number of computing nodes. However, a large flow of server requests may limit the Desktop Grid performance. In the paper we present a game-theoretical model of task scheduling in a Desktop Grid. The model allows to consider the trade-off between the server load and the total time of computations. The solution is illustrated on examples.