ASIP servers can peacefully coexist with NAT routers on the same Mac. I'm running an ASIP server at home with IPNetRouter installed on the same computer. Has worked excellently.
Although, if the option had been available to me when I started my home LAN, I would probably have gone the hardware route with a router/switch combo, like the newer models from LinkSys and MacSense and such. Because the biggest complaint is that crashing my server crashes my NAT router ... luckily, it happens very infrequently.
Jeremy J. Reichman, aka "Jaharmi"