I have windows 7 professional along with other LAN users in my home. We all share the same network connection as in "LAN", and it would be really nice given the sharing of bandwidth to see what network resources are being used. However, as the user posting this question mentions, you only see yourself when going to Task Manager, view users, Networking. I even installed a "Link layer topology manager and drivers on my network as Windows suggested that was required. Given we have a 300mbs DSL connection and a 1 gig router, it would be nice to know when a housemate isn't on Netflix, or trying to watch YouTube as only one of us can watch at a time. It creates feuds... so why did I buy WIN 7 Professional along with the others when I can't see a simple thing like bandwidth usage, let alone messaging a housemate?
in Switched networks (e.g. using a router), traffic goes directly where it is needed and does not pass through all the computers, so windows is unaware of of what's going on, so that solution won't work.
You need to get a router that shows you bandwidth graphs and monitoring from its web interface, such as a router that supports Tomato firmware. This will require some effort on your part (buying a compatible router and flashing it to tomato shibby or toastman ideally). There may be high end routers that have bandwidth monitoring / graphs built in so you don't have to figure that part out if you get one of those.
As for communicating internally to your housemates, consider getting a LAN messenger software like Softros. This works even when your internet is down, and requires no accounts or passwords.