There is an issue with Desperados: Wanted Dead or Alive.

The intro video plays perfectly, when the game starts however everything is going real slow.
The train at the start it takes some time to reach to the station and stop. Cooper moves very slow too. Why is that?
I've noticed the exact same problem with the original Desperados, not just the GoG version.
Is there a compatibility issue with Vista?
What if I change to Windows 7?

I remember having this issue on Win XP at one time, but I'm not sure what caused it. It disappeared after I upgraded my computer at some point.
You have checked all the compatibility modes, right (win98, win95 etc.)?
Also, update your gfx drivers, but that's a no-brainer.

edit: Oh, and the GoG version reportedly isn't patched for some reason, get this: [url=http://www.fileplanet.com/64352/60000/fileinfo/Desperados:-Wanted-Dead-or-Alive-v1.01-Patch]http://www.fileplanet.com/64352/60000/fileinfo/Desperados:-Wanted-Dead-or-Alive-v1.01-Patch[/url]
If the problem persists, apply a crack (from, say, gamecopyworld. Don't worry, it's clean). Cracks often fix problems, as absurd as it seems.

Desperados from GoG seemed updated to me.

Anyway, when I had the same problem with the original, I applied the latest patch & crack but no changes were made.
I've already tried compatibilty changes with no success.

Maybe I should try it with Windows 7.

Depending on your install routine . . on Vista / Win 7 . . you can get a partial install or some disk read / writes can be blocked. My first suggestion is to make sure you have the game shortcut set to run as an admin and to make sure you have the latest video drivers installed.

Here is a link to my suggestions for installing on Vista / Win 7. Even though it's a different game the info is relevant to all game installs on these two OS's.

There is a forum here at GOG just for this game. You should of posted there.

I had the same problem. My machine (dell xps 1340) has integrated+dedicated graphic card. Problem solved by turning off SLI mode .)

What's this SLI mode and how do I turn it off?

On Windows XP the trick was to disable DirectDraw acceleration from DXDIAG.

Replicating this trick on Windows 7 is a little more complicated and involves forcing DirectDraw emulation via the Application Compatibility Toolkit.

I think the GOG version already implements this workaround though? Does with me.