bandwidth blues

i am wondering if someone could tell me a program that can monitor the amount of internet traffic a particular computer on the network is using and then either decrease the bandwidth or restrict that user...?

im lost... the situation is my brothers mate moved in and he is using all our bandwidth... we only have 3GB download allowance each month and that doesn't last long on cable... i can't just cut him off or he would complain to my olds but i want to slow him down or put a download allowance on him.

thaanks

note: im running on a cable connection that is shared over our home network using ip masquerading with iptables... the fella has his own computer plugged into the network

>> using ip masquerading with iptables

Then yes, you can implement bandwidth throttling. Don't ask me how, you are supposed to search google for that.