So is your set up a single PC that is physically attached to a modem via a ethernet cable?
c: Figures of usage, my own usage - like, my totals in the event its the isp pulling some didgy shit, which I wouldn't put past THEM either.
For this I use Bandwidth monitor Pro - ver simple to use.
Theres lots of programs that can tell if your what Pcs are attached to your network.
This one finds the
MAC ADDRESSES on machines on the network. There prolly free ware version of similiar programs.
Hope this is a start.