I had the same problem when I started using CIS.
What I did was to create a rule in the Global settings to "allow TCP/UDP IN" from each MAC address of the other PC's. Then in the Application Rules I had to set SVCHOST and SYSTEM to outgoing only but then also add the same "allow incoming TCP/UDP" for each MAC address.
I also then had to create an allow UDP 192.168.1.1 -> 192.168.1.255 in Global, so all the PC's would show up in Network Places.
There is probably a much easier way to do it, that i'd also be interested in.