Clean your HD and all the previously said stuff. I think that it's most likely a virus/trojan/wierd cookie(?) that is downloading something as soon as it has access to the internet. When you connect, kill everything except your one connection and try <Start> - <Run> - <Command> - <netstat> for a list of your current connections and ports. Solution is AV software and a complete wipe of the harddrive. Then install everything while NOT connected to the outside. Check other computers on your network as well pehaps? Last unprobable possability is spywear of some type.