With NETGEAR FVS338 you can setup separate bandwidth profiles for services you allow through the firewall, but not on a per mac/IP basis as far as I can tell. You can have the profiles set to work on a a group basis or, possibly more useful in this case, an individual basis so if your profile is designed to limit port 80 traffic to 100kbps, each LAN side IP that makes a port 80 request would be limited to 100kbps, rather than 100kbps overall.
Something else to consider perhaps, a managed switch that allows you to set the rates for each port?