ok, I got a pretty much similar problem...
There's the situation, my PC is connected to the internet (well, duh) via built in network card, I installed a second network card, and plugged my sister's comp (next door) into it, to give her internet too, it all went well, and sharing internet works... until she got that blasted webcam and started chatting for friggin HOURS (up to 6 hrs of non stop noninformative bullsh... EVERY BLASTED EVENING)...
my net speeds fall more than by 60% of what I get in the morning, when she's not on skype. how can I limit her without having to choke her boyfriend with that webcam's wire to prevent him from giving her another one?