I like to share our broadband modem and access Internet from the second computer. The 2 computers are not connected to each other. I am considering setting up a network of these 2 computers using a wireless access point and 2 wireless network cards. I assume the access point and the braodband modem will be attached to one of the computers and the other computer will be able to access Internet through the access point. Is there any other way of sharing the modem eg. using adapters/ extensions, like sharing the telephone line?

Why don't you just buy a router and share the internet connection between the two computers? The router will be able to handle multiple computers (depending on how many ports you got with the router). Otherwise, with your current setup with just the modem, you will only have room to connect to one computer and make it act as a gateway in order for the second computer to connect. With the router, each computer is independent, where as the gateway aspect will require the first computer to be on in order to go online.

If you want one computer connected at any time the internet is being used on either computer then all you need are two lan cards and a crossover cable.