dynamic DNS and hostname resolution

[Marvin [GodfatherofSoul] Bellamy]

I'm slowly setting up my network to host some public services with 
TWC/RR and a dynamic IP.  My firewall will route connections to a web 
server and email server inside my network.  My question is, how do I 
handle resolution of the public hostnames www, mail, etc with DNS?  If 
someone connects to my firewall/router, does IPNAT (and the packet 
routing to the correct server) take over before the DNS query looks for 
the IP of the server?  This is new ground for me, so my question might 
not even be clear.  I can provide more info on my setup if need be.