how to limit bandwidth?

hi, i'm new here. i have some problems with internet networking. my office has several connected computer, and all can connect to the internet. Recently, some of the pc has exceeding the internet bandwidth (and i mean EXCEEDING), and has cause the entire system to slow down. it's been going for like 3 months, en i cannot trace who used caused it! is there any way that i could limit the internet bandwidth of a certain computer, or somehow control it? we could monitor the bandwidth, but is there any software (or perhaps freeware) that could limit the usage of bandwidth or perhaps force the computer to limit the bandwidth? i hope someone there could help me, because my boss have been on my back...

thx in advance

ps:i dont have any server computer in my office, the server computer is located elsewhere, so is there anyway i could limit the usage of the bandwidth without computer server?

You could try a packet sniffer program like Ethereal

thx for ur advice, i've already found a freeware that could limit the usage of bandwidth, but it can only deal with 3 user... hei, at least it work for now...

pleas how u do it pleas send me link or name of this great program my email is my007ms@hotmail.com i will be so greatfull for u i need it

A good program for limiting the bandwidth usage of one computer is NetLimiter.