In this paper, we address the problem of packet forwarding in multi-hop wireless networks of nodes equipped with multiple antennas. Through the use of MIMO (multiple-input multiple-output) technology, the physical layer is able to superimpose multiple concurrent information flows, thereby increasing the communications parallelism in the network. We propose a cooperative cross-layer scheme that integrates distributed incremental redundancy hybrid automatic retransmission request (HARQ) error control with routing in order to increase the efficiency of the transmissions and decrease the interference load in the network. In the proposed scheme, next hop relays are opportunistically selected during the HARQ process in order to avoid overloaded receivers and guarantee the geographical advancement of the packets. Thus, cooperation is used to both strengthen weak links and select the path to the destination. Numerical results are presented for a specific instantiation where a layered space-time multiuser detection (LASTMUD) transmitter-receiver architecture with spread-spectrum signals is implemented at the physical layer and packets are encoded with a linear erasure code (LEC).