to monitor traffic on any given interface you can use nload. like so:
where eth1 is your ethernet adapter or adsl connection (ppp0) or whatever. I take it as a given you know how to install nload on your distro
to chat in lan you can use Winpopup LAN Messenger. It runs with wine too, i think. You could also set up an irc server on a computer and use whatever client (xchat, mirc, irssi) to talk with people in your lan.
