ok erm.. this is my deal.

i have my router forwarding port 80 traffic to my 540c with a fixed ip and running mac http as you are.

i have the haddodock.no-ip.biz domain - from there i run the no-ip app on the 540c, which syncs my ip to the no-ip service and traffic gets to me.

i have not played with nor ever needed to play with the dynamic dns settings in my router, which i have always found to be a pain to set up.

my way is easier i think. however if your machine ip and your external (visable to the internet) ip is static then you can do without the no-ip app.