Two Networks Computer to Computer and a regular internet connection

Can you explain what you are trying to do? I have two networks, one g and one n, but I use two routers on one cable modem. I take it you do not have wireless, is that correct?

 

As above, what is it exaclty you are doing?

If I understand correctly, you want a computer to computer network, and share the internet connection?

If so, simply go to System Preferences -> Sharing on the computer you wish to take the load, and turn on Internet Sharing. You can specify how you want to share the internet (Airport, Firewire....) Since you are talking about a computer to computer network, you might as well pick Airport. But the internet accessible computer would have to be on the net via wired (EG Ethernet/USB etc) , as you are already on a Wireless network (the computer to computer)

Alternativly, you could share the internet connection via Firewire, and then you would be free to connect to your wireless router with the computer that is sharing its connection.

 

The normal and most common setup is to connect a rounter (wired or not) to both your internal home network and to your Internet service provider. Even in the case of someone who has only one computer and a router there are two networks. (1) the "Internet" that is on the upstream side of the router and (2) the wire between the router and your computer is a "network"

The job of a router and the reason it is called "router" is that it's function is to move data from one network to another, to "route" packets.

I think what you are asking is how to expand the simple (#2) network. It's easy. Most routers have multiple LAN ports just plug the second computer in there.