i have 5 IPs on my service
i have 2 servers hanging off this service each one needs its own external IP (for mail etc)
my options were:
get a dumb hub assign static ips to north facing nic and polug them both into hub
get a linux box with 3 nic's in it to deal with all the traffic
get 1 hub and 2 routers hanging off it one for each server
get an expensive hardware firewall that does multiple NAT or allows me to have more the 1 external IP such as a sonic wall etc..
no cable routers will allow you to do what you need adsl routers will
anyway i went for the cheap hub and 2 routers option as a i had an old hub and router to use already