Monitoring network data throughput?

I do a lot of FTP file transfers with FileZilla, and like to leave the transfers going while I’m away. But my roommate, who uses the same Internet connection/router, likes to stream video from Netflix and Hulu during that time and I don’t want my transfers to slow down his connection. I’d love it if I could somehow detect how much bandwidth is being used by other computers on my network and pause my transfers when the network is in use by others. Any idea how I can do that? Thanks a lot.