Need a new gadget!

hi i need a new gadget for monitoring how much data ive downloaded with maybe in the last week/month/overall if it is possible or if one allready existed?
The reason for this is a friend or mine had his line capped so he rang thru to his ISP kicking off and wanting to know why. well it turned out he had breached fair usage right by downloading 200GB last month 160GB month befor and so on! so maybe a gadget like this could help downloaders keep an eye on how much in total they are downloading!

Do they monitor network traffic (IE if I stream to my PS3) or do they give actual internet dl/ul activity?

reason I ask is I used to have a similar tool when I had a 40gb CAP/month, and had it set to alarm at 35gb, but because it recorded network traffic, by the end of the first week I had hit my limit.

Only works for the PC it is setup on, for example, I have:

Main PC wired - Net Moniter installed and working
2 x XP laptops wireless
1 x Ubuntu Desktop wireless
1 x ubuntu netbook

Net monitor only records the internet traffic on the main wired pc...I need a tool that records the actual internet usage that goes to/from my ISP (TalkTalk)

It also includes sreaming data from my PC to my PS3.