In this paper, the combination of linear network coding over a finite field and beamforming for a multiple-antenna network is studied. Assuming a multicast transmission scheme and a decode-and-forward protocol, optimal beamforming strategies for the network nodes are derived for a certain class of interference networks. An efficient algorithm is presented to calculate the achievable rate region of these networks. The sum power for the transmission of the multicast information is minimized under rate requirements. The proposed approach is illustrated by one important scenario.