After some days searching over the web for a solution to the network game, I've managed to solve the issue and play for hours with two other friends from another city and we hadn't felt any lag or desync errors. We've activated the ipx through DOSBox, connected to each other pc, and still couldn't find any game. I even posted here the problem but had no reply. After reading the working solution that use the Constructor cdrom, I've realize that we needed to make DOSbox execute the tunneling process (ipxnet startserver) automatically at the game launch. So we added the ipx commands on the [autoexec] section of dosbox.conf and it worked!
Here's the step-by-step:

1 - Open dosbox.conf (it's located at the main folder of Constructor (gog.com version) with notepad
2 - Scroll down to the end of the file, where the [autorun] section is located
3 - We need to make DOSBox execute the commands at the game launch, so we need to add the following commands before the line that contains "game.exe":
ipx = true
ipxnet startserver 'port' (this line is needed for the player that will host the game. Replace 'port' with the port you want to use. The default DOSBox port is 213, but I think that you don't need to specify a port. Anyway, it worked for me with the port).
ipxnet connect 'ip' 'port' (this line is needed for the players that will join the game. Replace 'ip' with the hamachi ip of the host and 'port' must be the same port the host is using.
4 - The host start the game first (so the DOSBox server starts and the clients be able to connect). The other players can start the game after the host.
5 - The host start a new network game and the other players join the game.

ps: I'm going to try to add all to commands (the host and client ones) to my dosbox.conf to see if still work without the need to edit every time the player who will host the game is changed. And I think the line "ipx = true" isn't really needed, because ipx is already activated on Constructor (gog.com version), but I use it and I had no problems yet. This solution worked on Windows 7 x64.
Sorry about my english, hehe.

In short, the host will have the [autoexec] section looking like this:

[autoexec]
# Lines in this section will be run at startup.

@ECHO OFF
mount C "."
imgmount d "const.gog" -t iso -fs iso
c:
cls
cd \
ipx = true
ipxnet startserver 'port'
game.exe
exit

and the other players:

[autoexec]
# Lines in this section will be run at startup.

@ECHO OFF
mount C "."
imgmount d "const.gog" -t iso -fs iso
c:
cls
cd \
ipx = true
ipxnet connect 'ip' 'port'
game.exe
exit

I hope this works for everyone. :D


EDIT: The dosbox.conf file is now called DOSBox 0.74 Options in the latest version of DOXBox. Thanks to Boss_Duck for the report.

I cant find dosbox.conf I think it has been updated now :(

But thanks for the help but I cant make it work now hmm!

Sorry about the late answer. I've just installed the latest version of DOSBox (0.74) and now there is a file called "DOSBox 0.74 Options", it's the dosbox.conf now.

I just want to say that this makes it possible to play over regular LAN as well, not only hamachi. Thanks for the guide!

Thank you very much for this post!

Hello.

I would like to play Multiplayer. I know how to do it I have friends which who I play this game.

If you are interested, please add my Skype : Agog_Fr