A friend and I are combining our limited intellect to try and slash each other up in the arena.

We can't get Hamachi to work or using our real IPs to work either.

Whats the solution?

I managed to play with a friend through tcp/ip some years ago.
It was not the gog version, though.

I am no expert, but i believe if you are having trouble with tcp/ip the game is probably not the problem.
Check your firewalls permissions and if any of you have a router port-forwarding might be necessary, but unfortunately
i have no idea what port the game uses.

Sorry for the late reply.