Such P2P programs can cause internet issues because of their file sharing with the entire world.. It's also a reason why some types of universities and ISP's tend to block IPs that are using such.. Easiest solution, have the roommate get their own service..

Another option is the router/modem doesn't fully support Vista.. We've found a few such issues which were solved by updating the firmware on the router/modem. Visit the manufacturer's website and see if newer firmware is available..

Hope this helps.