Here's what you do assuming your DVD drive letter is D:

Step 1.) Make a folder in your C: drive called "dosgames" (all one word without quotes)
Step 2.) With the Warcraft II CD in your DVD drive, open DosBox

From here all of commands I give will be commands you type in DosBox. The quotes aren't to be typed.

Step 3.)Type "mount c C:\dosgames"
Step 4.) Type "mount d D:\ -t cdrom " (this may not quite be right, it's a long time since I've installed a game in DosBox straight from a disc rather than using an iso)
Step 5.) Go to the DVD drive by simply by typing "D:"
Step 6.) To install the game, type either "INSTALL" or "SETUP"
Step 7.) The rest should be self explanatory. If you want to make things easier, add the mount commands to the autoexec section of your DosBox conf file. 😀

Also, here's the official 60 second guide. 60 seconds guide to getting your game to run in DOSBox It basically covers what I explained here, but in greater detail. I just wrote my steps from memory as I didn't feel like bothering to look for the guide at first.

Thanks that worked perfectly!