You could use bandwidthd to graph all ips. You basically specify subnet(s), and it will use promiscuous mode to graph bandwidth up and down, as well as some basic protocols i.e, HTTP, VPN, P2P. It works very well. I had about 52 subnets specified on one box just running Debian, on a mirrored inet port, and it runs very smooth. This will only graph though.
To see in realtime, ntop would be nice, or perhaps some sort of netflow. Zeroshell already has iptraf readily to use.