Has anyone gotten multiplayer to work? If so, I would gladly throw more money at the chance to play multiplayer Cossacks again, although the steam versions fail.

Yup. The only thing I had to do was letting Cossacks through Firewall. I mean TCP/IP ofc. If u can't see each other games you probably need to activate TCP/IP protocol.

We've tryed to use Hamachi for playing multiplayer. We've succeeded to run multiplayer game and even to play for 10 minutes before synchronization problems. We could only see each other in a list of available games, but could not join. We completely reinstall cossacks and hamachi but without any success

So,
Hamachi
Direct TCP/IP or Lan TCP/IP could work:)

UPD
Use GameRanger for playing this game:)

I know this is an old post, and I'm only responding because it got bumped by the OP

I myself had this same issue (sort of) and found out that a BELKIN router will NOT allow local games to connect. It's a NAT Firewall issue. The way I solved this (though I still can't seem to play a game on the same network (when the other computer joins it kicks me and when I join it kicks the other computer) but at least I got it to connect to each other) was to set up a DMZ with my router for one computer. This of course puts my computer outside my routers firewall and then allowed the games to connect. So ya might check yer router.. that might be the problem.

My experience:
I can play LAN games only with "Run as Admin" turned OFF.

EDIT:
If you want to play with just two people just hook those two computers up directly with an ethernet cable (turn any wifi connections off).
Might want to try turning off the firewalls too.
Run it in compatibility for XP SP 2.

Okay thanks, I'll try it out when I get my other comp fixed.. my fan went out on it and I am afraid to turn it on now.

Old topic but for those of you that are still having issues with multiplayer play:

the easiest and most reliable way is to launch a game is to use GAMERANGER. Then if you are still having problems you must set some port forwarding on your router (search the web for that, you'll find easily which ports to open).

As for decreasing the multiplayer game speed, use a CPU downclock tool to set the CPU speed to minimum possible, on all computers in the multiplayer game:
- ThrottleStop (for intel)
- Catalyst Control Center (for AMD).

Tom