bandwidth usage by IP address

[Justin Zygmont]

Does anyone happen to know of a program that can monitor the bandwidth 
usage of my LAN by IP address?  All the the client PC's use static IP's 
and it would be useful to see how much traffic each one is using.  The 
only thing is the need to use SNMP instead of an ethernet device 
listening on promiscious mode, because the network device is a lynksys 
router and the network is on a switch, not a hub.  It doesn't seem like 
MRTG can give a summary of usage by individual IP addresses?

Thanks..