Getting norton gateway to work

Ok,

      If I get this correct, i should be able to connect to the gateway from a outside source and access the computers on my network that are attached to the gateway correct?  I have the gateway installed but for some reason I can't see any computers when i add a subnet? my current network configuration is

Gateway: 192.168.20.1

Subnet: 255.255.255.0

All of the computers that I'm trying to acces are ips 192.168.20.100-118. I put into the gateway as a subnet 192.168.20.0 and it still can't see any of the computers. What might i be doing wrong?

Thanks