I've spent hours wrestling with mine, and if yours is anything similar I suggest you login to the router, usually by typing 10.0.0.2 into the Address Bar of Internet Explorer or Firefox, and authenticating (default user Admin, password conexant).
If necessary press Advanced Setup, and then Virtual Server on the left.
Enter 80 in the Public Port box;
and 80 in the Private Port;
Port Type TCP;
and then in the Host IP address the IP address of the computer running Apache, probably something like 10.0.0.x.
In the left bar, click Save Settings, and then Submit. Now try it.
I'll be happy to carry on helping by the way, if you don't get that just say and I'll make it easier.