Hmm, not quite sure what you're trying to do?
First off, I recommend you either run iptables commands from the command-line, or use a bash script to run the commands for you.
You're editing the iptables-save file, which is NOT the way to do it...
And when it comes to the forwarding you're trying to set up, why? Why are you forwarding requests from the external interface to the internal?
This looks very strange, especially when you can setup apache (and probably ALL other webservers) to use both internal and external IPs.
And: If you disable the external IP, is it really a mystery why you can't ping it? Or did I misunderstand?
Hope this helps? If not, I suggest you describe the problem a little bit. What are you trying to do? Do you have a vhost on the internal IP that you want to have working on the external ip?
I get the feeling this is an apache config problem, not iptables?