Not knowing how you're connected to the Internet, and not knowing how this other user connects, it's hard to help. But, if you're connected to a wifi network via your
wireless router and your connection drops when this other user connects to their
wireless router, your problem might be that both wireless routers are using the same channel. Here is some more info: http://www.howtogeek.com/howto/21132/ch ... ss-signal/
(you can ignore the windows stuff).