A quick update.
The good news is I haven't forgot about this thing. ;)
The bad news is - I haven't found (yed) the disc I was talking about.
Buuut, I stumbled upon other disc from the same issue of this gaming "magaine":
I think (and hope!) that the disc with the demo is still somewhere at my parent's house. I'm gonna keep looking. :)
According to the PCGames website Machines demo was present on the disc of the 05/1999 issue: