Zone alarm only lets you use one computer as a 'gateway to the internet' to allow another pc to connect to the net if you are using zone alarm pro.
messing about with 'pc gateways' and the like is a pain in the backside - either you get file transfer between pc's and no internet, or you get internet and no file transfer - that's my experience anyway.
Connecting via an ethernet hub/router is more or less 'plug & play'.
Have you manually assigned ip and dhcp addresses for these computers?
I know my router default IP was interfering with my pc's default ip - so I had to change one, and set an IP range on the router so if any other computers were connected to the network they would not have problems.
Most of the time you can set it to automatically assign from a range of IP/dhcp or whatever and it just gets on with it.
http://portforward.com/default.htm handy site for this stuff.
If I were you I'd start from scratch with your connection install.
