The keyword you're probably looking for is "name based virtual host". There are two ways to do virtual hosts in apache, one being based on the IP address, and the other based on the name of the web page the browser requests. Very old browsers (we're talking mosaic) might not have supported name based virtual hosts, I don't recall. The only real reason these days to not use them is https sites have to have their own IP address. The short answer is to just forward port 80, and have both domain names point to your public IP. Then configure apache correctly, and everything should work fine.

If you need more help, post what it's doing specifically, I'm sure someone can help.

Matthew