Set Client Speed 256 Kbps

I have Internet Caf? with 11 PC and using 2mb Bandwidth limited access (35 GB) Internet line of BSNL ISP. The problem is when only single user using internet in caf? access full bandwidth and doing unnecessary downloads and that is my loss because of limited access.
I think if I can set access limit to all pc (client) @ 256 kbps then stop that unnecessary download my loss. Can it is possible but how can some one help me out Pls???..
About My Cafe Setup All Client access internet through share router in network (all network client directly attached to Huawei MT841 router using network switch) and Client side os is windowsxp professional sp2