A cooperative network where transmission between two nodes that have no direct link, but assisted by many relays is considered. We assume a broadband system, such as OFDM, modeled by multiple parallel Gaussian subchannels between the source and each relay, and also between each relay and the destination. We formulate the optimization problem for joint power and subchannel allocation under a short term per-node power constraint to maximize the instantaneous total transmission rate between the source and the destination. To solve this optimization problem, first we find the optimal power allocation for a given subchannel allocation. Then we focus on a greedy algorithm that jointly allocates subchannels and power. Simulation results reveal that our proposed algorithm results in rates close to the optimum allocation.