Monitor Internet Usage

Hi all,
I want to setup a small ISP.
I will use Canopy to connect some clients.
I will most likely use ipcop as a gateway to start with because of costs.
Can someone tell me how they would monitor a clients internet usage.
Most ISP’s can tell you what sites you have been to and the total internet usage you have used. Some can even cut your internet speed down to dialup speeds once you have used it up.
I have checked out IPCop and there is a addon which helps monitor usage but it is not very reliable and doesn’t show where a user has been.

Does anyone know a good way to achive this ?
Any help is appreciated.