Correct me if I am wrong but you want to:
a) Have four computers connected to a hub in a such a way that you have a small network between the four computers.
Only allow your computer a connection to the internet
The only way I can think of accomplishing this is to buy a secondary network card. Setup one connection to receive and IP automatically, and then you would probably setup the other one as a 192.168.0.X ip on each computer. However, even there I am not sure how well it would work.
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