If you can bear with me, I'll get onto this when I get home from work (probably in about 2 hours, or so).
Ewen :-)
Gday silverchip,
Sorry I took a bit longer than planned to get back to you, but work has a nasty habit of getting in the way.
This is a long one, but please read through this completely to make sure you understand the overall process.
To make sure my reply makes sense, we'll make the following assumptions;
1. The IP address of the first NIC in the desktop is dedicated to your internet connection
2. The IP address of the second NIC in the desktop is 192.168.1.1
3. The IP address of the NIC in the laptop is 192.168.1.2
4. Your LAN is correctly established through the idiot-sourced switch

5. You have correctly set up proxy / internet sharing software for the 192.168.X.X subnet
6. CPF has been installed on the laptop
7. Your internet connection is
not active until CPF is installed and configured on the desktop
If these assumptions are correct, you should do the following;
1. INSTALL CPF ON THE DESKTOP! Do you only have a lock on your back door?

2. Configure CPF on the desktop first, as it is the entry/exit point to the internet
3. Configure CPF on the laptop
4. Activate the internet connection on the desktop
5. Test internet connection from the desktop
6. Test internet connection from the laptop
7. Continue testing to make sure the connection doesn't drop out
Once CPF is installed on the desktop, the first thing you should do is to use the Zone Wizard to define the zone that is your LAN.
The zone wizard will detect the two network cards in your desktop. MAKE SURE that you define the zone that applies to the NIC that is connected to your LAN (192.168.1.1) and not the one that is connected to the internet.
STEP 1
You should define the start address of the zone as 192.168.1.1 and the end address of the zone as 192.168.1.255. This will allow you to add computers to your LAN, without having to change the zone settings. You should give this zone a meaningful name, like Home LAN, so it is readily identifiable in any rules you manually create that use it.
STEP 2
The next step is to add this zone as a trusted zone. This will create network monitor rules that will allow traffic across the machines that make up your LAN.
You can check what rules have been created in the Network Monitor section of CPF.
STEP 1 and STEP 2 should now be repeated on the laptop. Please note that on the laptop, it should only find a single NIC with an address of 192.168.1.2 and this is the NIC that will be used as the basis of LAN zone. You can give the zone on the laptop the same name, as the zone names are local to the machine CPF is running on. The default rules created by the wizard allow for all ports outbound on the local LAN, so the port designation for the proxy shouldn't matter.
You should now test things like access to shared folders and network printing (assuming that these are set up, of course).
If these work correctly, activate the internet connection on the desktop PC and test connectivity.
You should receive popups from CPF as each new application attempts to access the outside network (internet).
If everything is hunky-dory on the desktop, repeat the internet tests on the laptop. You will get the popups again, as CPF is local to the machine it is running on - its a PERSONAL firewall not a LAN firewall, after all.
Keep both PCs running to test the connectivity problem. If the internet connection drops out on the laptop, the first thing that should be done is to check whether the intenet is still connected on the desktop, as the laptops internet connection is merely an extension of the desktop PCs intenet connection.
If it is still running on the dekstop and not on the laptop, AND the configuration of CPF is identical on both machines, logically there is always the chance that its the proxy software stopping access and not the firewall. I'm not saying that CPF can't be at fault, but the proxy software is another link in the chain and must be examined.
To test the theory, you could install the internet connection and the proxy on the laptop and then reverse the configuration so the desktop is connecting via the laptop. If the same failed condition is reached with the laptop still working and the desktop now stopped, the proxy software is still the common element and the CPF configuration can reasonably be ruled out. Not entirely, but reasonably.
Please go through the FAQs on setting up the network rules and the rules for specific applications. There's some really good hints 'n' tips in there, and they've been created by CPF users based on real world problems.
As previously stated, the proxy should be absolutely immaterial to the firewall on the laptop. CPF is only concerned with the validity and legitimacy of the inbound and outbound connections on the machine it's running on.
I realise that this is a LOOOONG posting, but it is in your best interests to get your head around the basic concepts of how CPF, and a personal firewall in general, works.
If any of this is not clear, or if I've missed a bit, let me know and I'll rectify.
If this does solve your issues, please post the result back here, so others can benefit.
Hope all this helps and good luck.
Ewen :-)