hi
you would like to see all traffic running from and off the internet ? well I recommend get a 10/100 HUB . plug it between your cablerouter and your other switch and rear equipment . on the hub connect a system ( I prefer w2k -> more stable und reliable) and let ethereal or tcpdump as recommended running on this machine. only on a hub you see ALL Packets going and coming into your network. all other equiment should be connected on your switch. only the sniffer pc goes with the hub !
maybe a little help.
skarsatai