Internal and External website

I have a Win2k3 server setup with with AD domain setna.net. I have two websites setup in IIS, one internal and one external. I want www.setna.net (external page) to resolve to website running on port 8100 and setna.net (internal page) to resolve to port 80. I have setna.net working and it loads a page saying internal. I don't know how to setup dns to answer www.setna.net. I tried to make an A record pointing to my external ip (68.168.239.97) but that points to port 80, i need it to point to 8100. I have also been messing around with port forwarding on my linksys router but have yet to get it to work.

setna.net 80
www.setna.net 8100

Router Port Forwarding
EXT ---> INT
80(blocked) 8100 tried to push internal www.setna.net to port 8100 to display external page

8100 8100 external port for external page

8080 80 used so internal page can be reached from outside using ip:8080