sniff cable modem

i need to put a pc in between my modem and network for sniffing network bandwidth monitoring etc.

have a netgear certified modem. my current option is dropping a 100mb hub off modem, plug a 5 port 1gb switch into that. then plug everything into switch.

have everything gigabit inside cate5e. my inbound speed is 240 mbs. id perfer not to lose that. im not using modem wifi but asus rog wifi router. any options?