Open game. Select single player. DOS BOX opens and shuts down. Cannot open game.

same here, anyone help!!...

Just checked on my old Unibody MacBook and it crashes as well and I investigated for the DOSBox devs why it does:
The Warcraft config sets the fullscreen resolution at 1440x900. If that is bigger than your Macbook's maximal resolution (or maybe even the resolution you set your desktop to) DOSBox will crash.
The DOSBox devs will contact the GOG people so expect a fix soon, I hope :)
In the meantime, edit dosbox_warcraft.conf and enter your maximal resolution in fullresolution= (line 26). You need to right click on "Warcraft Orcs and Humans.app" and select "Show package contents". Then you need to navigate to Contents->Resources->game. In that folder the dosbox_warcraft.conf is located. Open that with Textedit and edit the line 26.

Let me know if that works for you!

same here

Worked great! Thanks!