First it is easier if you have a static address.
lets say it is 205.64.15.15
and your ipaddress is 192.168.0.2
and the router is 192.168.0.1
next got to the router
http://192.168.0.1
then enable port forward 80 in the router to 192.168.0.2
then make sure you have port 80 open on your box then
go to no-ip and set it up
then go here and and see if it is working
http://instantservers.com/tools/test_web.html