Need a way to monitor wireless bandwidth usage

I have a DSL connection that I am sharing with 3 roommates. When I agreed to share it I made it clear that major downloading had to be kept to a minimum or I'd have to stop sharing it because the speed would slow down to a crawl. Well things were fine for a while but everyones connection speed seems to have slowed way down and I need to know if its 1 specific person downloading to much. Is there a program that will show me how much bandwidth each person on my wireless network is using?

Thanks

1. I don't want to be nosey (obviously so)

2. I don't want to accuse anyone needlessly.

I aslo need exactly the same thing, have you found any software that can do this yet?

have u tried net traffic mon?
[http]http://members.shaw.ca/msamoila/[http]
it might be what ur looking for, im still looking for a better one...