Then how do I get the windowed mode to work?Or at least where do I type -no3d command?
Right-click on the icon you use to launch the game; click on Properties.
If the Shortcut tab isn't already open, switch to it.
In the Target box, after what's already there ("C:\GOG Games\Arcanum\Arcanum.exe") add -no3d
At the same time, you might want to add -scrolldist:0 -scrollfps:70
as well; this is a neat trick that allows you infinite scrolling, rather than being limited by your PC's perception score.
The whole thing should look like: "C:\GOG Games\Arcanum\Arcanum.exe" -no3d -scrolldist:0 -scrollfps:70
Save the change and launch the game, and see if this solves your issue. Best of luck.