i own a cyber-cafe and i'm using ubuntu 8.10 on client machines, i have a kubuntu 9.10 server. Apparently, the clients have been downloading way too much and heavy softwares during the time which other clients are using the same network. The only method i've been using to monitor the downloads has been to check what the clients do from one client pc to another. But this doesn't go well with me at all because i feel that i interfere with clients concentration once in a while ad its also cumbersome. So i actually thought that someone from this community will help me to know if there is a software i can use to monitor the clients' downloads from the server and limit them...to avoid the drastic fluctuations of the internet from time to time because of some wayward clients downloading heavy softwares on the same network.

if more details are needed, i will be available to provide.

thanks in advance

Various ways to go about this. You could either limit the network usage of client machines through iptables with following modules:
Or use tc on the server side
or even the above listed iptables modules.