My ISP cuts you off off you don't do anything for four minutes - but as Grab says, there are programmes tyat run aeround in the background doing things that keep them off yor back, if for example you are writing a long post online.

I've got one called NetMonitor which I got free on a magazine CDROM; here's a link to another Activa DUN Meter - th eversion on the link cost $15 - there's a free version on another CDROM I've got (and it does other clever stuff as well). You should be able to find a free version of something that does the trick without much trouble.