Your router may need to be set up to forward Port 80 (or what you specified) to your machines IP address.
Some routers also have web based management, which is usually set to run on Port 80 so this would need disabling too.
Finally, are you using the local machines IP address such as 192.168.0.2 or are you using the IP address supplied by your ISP (which you should be)
I am using the IP address found under network in system preferences.
How do I know if my Mac forwards to Port 80? Do I need to turn some kind of sharing on?
Any one else can you help with the web publishing?