Ok, here's what you probably need to do....
*Only on one of the machines*
Run ImpuleReactorOptions.exe in the /bin folder of Demigod.
In the port number boxes put 6133 and 6153.
This is make that machine use different ports than the other one, which is the likely source of the problem.
You may need to configure router ports if these aren't already opened. While proxy or NAT might get through, the performance is always better (even if marginally) if it doesn't have to do that.