Mod_Throttle how do you specify the action that happens when they go over the limit? Like i wan't it to do something like not display any page, or just return a page saying over bandwidth.

When I was using it, I did the following..

ThrottlePolicy Document 100M 1d

This allows up to 100 megs bandwidth a day. If they go over that though, it doesnt shut down their entire site. It simply disallows downloading of anything other than html and images attached to those html. In other words, after 100 megs, anything that's attempted to be downloaded that isnt called from an html page is denied. Links to download files wont work either untill that 24 hour period is up. Setting an amount per day is better than a monthly allowance anyway.