I need a way (whether it be hardware or software based) to resrtict the amount of data any one user can use in a monthly cycle. (i.e set one computer/user to have only xGB for the month and for it to reset at a certain date).

I will need to get a new router soon anyway... so if it is hardware based that isnt too much of a problem... but I would really prefer something software based if possible. If I could restrict the maximum speed the user can use at ony one time aswell it would be good... but its not a major if I cant.

So as usual... any ideas would be appreciated.