help…need help regarding network speed

i am currently working on a simple WAN network. I am using wireless radios to interconnect 5 sites. I have a low end linux router at the central station and workstations on the remote end. Each remote stations would have 3 to 5 computers. The thing is, speed is not that sufficient enough linking from a remote station to the central station. Using an application with a higher bandwidth usage wouldnt budge though the pipe. The throughput of the radios are 700 kbps. Do i need some additional hardware to pick up some speed? Please help….