Although I can successfully adjust the game speed in singleplayer mode, the options seem to have no almost effect when playing a multiplayer game in LAN. The game is just unbearably fast.
The predecessor, Cossacks, has the same problem.

Has anyone a solution to this?

Yes, I have a solution.

First, 'fast mode' and 'slow mode' does have an effect in multiplayer. The actual speed slider doesn't have an effect, however, that's true. The issue is that even using 'slow mode' the game will most likely run too fast, anyhow. Why do I say 'most likely'? Because this game is special in the way that the speed of the game is directly dictated by the speed of the CPU. Also, the game will try to sync to the slowest CPU in multiplayer.

What does this mean? Well, if the game is still running too fast there's only one solution; and that's to slow down the slowest of the CPUs further. This can be done by down clocking the CPU through the BIOS, or using Intel Speed Step - or the AMD version - if such is available. If so, you can set a CPU limit through the Power management in Windows. Aim for around 1200-2000MHz in either case using 'slow mode' (in-game).

So, will this make the game run perfect in multiplayer? No, but a lot better! Playable, yes.

Why not perfect? Well, because of the syncing done between multiple PCs with CPUs that's not equally powerful, and just the fact that game is super sensitive to any change in available CPU power. Like, if you move the mini-map in-game by dragging the mouse around in it, the whole game down on all the PCs connected to the game!

If you had a couple of the same kind of PC with the same specs (CPU mostly important) and at the right CPU speed, in terms of translated game speed, it might run close to perfect, as close it can come, anyhow. Having the same CPU speed (actual CPU performance) across multiple PCs might simplify the syncing between the PCs. However, I just tried with a 4.2GHz and a 1200HMz (down clocked) and the game ran pretty fine. Not perfect, though. There was a tiny bit of micro stutter (syncing, likely). But perfectly playable. Using the mini-map, as said, uses enough resources to slow the game down. Therefore try not to use it too much in-game.

The short answer is also that the game just wasn't really designed for multiplayer performace (yeah, it's a bit sad) , however, I hope somebody will benefits from this information.

I have found out something very interresting about the American Conquest engine today.

There's was a another game made with this engine, and that game was: 'Heroes of Annihilated Empires', also by GSC.

And in this game the devs actually added a 'contant speed regardless of FPS' option. Also, you can pick constant speeds of slow, normal, fast. So the engine is capable of a better solution for American Conquest's multiplayer, too.

It'd probably to an easy fix to make, sadly GSC is dead now, last I heard. But they should have added that option to American Conquest before they went under. Damn it. They should still make a patch, at least for the GoG release of the game! :(

That GSC died is their own fault. I have had personal contact with them on several occasions in the day that Cossacks 2 was out. They just laughed and waved the problems away as that they didnt care. There was a war going on in the forums as they screwed up so bad with the errors in Cossacks 2. That game rocked, but had some serious flaws. I loved that game!

Just letting you guys know that there's a program called 'BES that can limit how much a process is allowed to use of the CPU time. This is the single best solution for multiplayer. You only need BES, nothing else.

http://mion.faireal.net/BES/

Basically, you can use this program to adjust the speed of the game, in real time! Just don't go higher than minues '60', because that seems to affect the game negatively, otherwise it works smoothy. This is not a 'CPU killer' thus it doesn't heat up of your by 'killing' the CPU.

I recommand minus 50% for most moden PCs. If the game slowsdown too much later in the game (with many units), then turn the limiter down by alt-tapping out of the game. But be quick, the game will kick a person alt-tapped after something like 20 seconds.

Hippox99, thanks for your tool!

it works almost perfekt!

there is just a big an da small problem.
small one: mouse works not smooth.
big one: sound and music work not smooth. it sounds like the pc is overcharged with playing the musik.
Without sound game works almost perfectly.

this problem appears on the host pc. on the client pc everything works perfect!

Try to run BES as admin and try again. :) It's not my tool. I just found it. ;)

Hmm, sounds like you need to turn the limiter down as it seems like BES is maybe strangling the game too much. At 50% the sounds and mouse is very smooth on my PC, but try another percentage. The CPUs I have tested is both Core 2 Dues, maybe other CPUs will have issues with BES? I dunno.

Also, you mustn't use affinity (making a multi processor run falsely as a single core) because that makes the game less smooth, and it makes the mouse lag. I don't think the game likes affinity.