56K Internet sharing with 9.1

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Currently I have two macs. The one that is connected to the internet (through 56k) runs 10.2.X and the other one runs 9.1 and is networked to this mac directly through the use of a ethernet crossover cable.
I already can share files between the two but after finding the internet sharing option, I wanted to try it. I get about as far as clicking the "Start" button for internet sharing and then I do not know what to do next.

The internet computer's ip is: 10.0.0.2
the router is 10.0.0.1
The other coputer's ip is 10.0.0.3

Any help would be appreciated

 

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Just as a late follow up, I did get the modem shared. All I had to do was turn on "share internet" in mac os x and set the attached 9.1 computer to a dhcp ethernet connection. Pretty simple.