I'm new here, please be patient with me

I was looking at the NAT features in ASL and while Masquerading makes perfect sense I was thinking how I could make the DNAT work.
Scenario: My external interface on ASL has 63.63.63.63 and I would like to forward all HTTP Traffic to a webserver running on 192.168.1.2.
Now, if I choose DNAT I can choose a service type (HTTP), then I select internal address but then I can't type in the IP and/or port of my web server but instead I'm am given a list of services to choose from again. Where do I enter the computer I want to forward to ? Please excuse me if this is a really lame question but I'm truly puzzled.
Many thanks for your help !
This thread was automatically locked due to age.