How To Restrict On One Connection

I have an Intel Pro 1000 PT dual gigabit port NIC which I bought so that I can have one port plugged into the modem for my internet and the other plugged into the other network so that other computers can access files on my computer. The problem is that the data allowance on the internet connection for everyone else is very little so I don't want my computer to access the internet through the second connection. The primary reason for the file sharing is to stream movies over the network so I don't want to be enabling/disabling all the time. I have already tried setting a static IP and blocking it through the router on the secondary network but then I have all sorts of issues with applications in Windows (I'm using Windows 7 64) trying to access the net through the other connection, not getting through the router and timing out instead of trying the other network connection. Pointing the DNS to the static address on the secondary connection wont suffice either because it's torrents I'm trying to stop from downloading through the other connection not browsing. I've done a bunch of searching, what I'm trying to find out is if there is a way to disable internet but allow LAN traffic on a network connection. Hopefully with it being set in the software Windows will then always seek internet through the other connection.