How can i moniter clint pc Data trasfer in internet..??

My Dear Friends..!!

I have a cafe how can i control or watch My Data Traster Rate of my clint pc..??

i have a cyber cafe...!!
I have win 2000 Server ..!!

and 9 clint pc have 2000 pro.!!

now i want ot watch which computer use how much data transter send recive...!!

becoz now a days cable is comming with price with per MB..!!

so now i want to watch which user use how MB per Hour..!!

Thanks

Prakash Patel