Oki, here´s the setup.
I´d like to set up a network at a friends place. There´s gonna be something like three or four computers running on it sharing the same internet connection. (She´s got a 10mb line)

Last time I was there I connected and directly started downloading a firewall, (blackice) when I was done installing it I had an intruder poking around inside my puter (not including the outside scans)

My thought is that instead of setting up the switch directly to the 10mb (and leaving every puter fending for itself) I want to put a puter between the wall and the switch. (with tiny firewall)

And the question is, can a normal sniffer "notice" that there is a larger network behind the puter with tiny firewall (and a second network card)?

Other security ideas are well received aswell