(1) Quit Zonealarm on all PCs before everything set up. Once set up is done, you can start zonealarm.
(2) All machine should belong to the same workgroup, i.e. the same workgoup name. The one name which does not cause any trouble is "WORKGROUP", strange but true.
(3) I assume that you are using a router for your network. It is necessary for a network with more than two PCs to use a router.
(4) Enable DHCP in your router setup and set all PC's network TCP/IP properties to get IP address automatically, i.e. dynamic IP address.