port traffic on a second networkcard

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 :D

I have some experience with Windows based firewall boxes at home... all of them where either instable, not free, consuming many resources, or simple didn't work right... If you want stability, use a simple Linux box with two NIC's as firewall and router. You can use a complete Linux distro to do this or use some floppy based 'mini' linux to do that. Like swfloppy or BBIagent. www.BBIagent.com

If the firewall performs NAT, the normal SK-scanner will not detect computers behind your firewall. While they are on different nets --> 1st NIC : public IP from ISP
2nd NIC : private IP assignd by your DHCP box or manual assign

Tiny uses NAT, go for it.