The dos and windows version use different resolutions. I believe it to be 320x200 for dos and 640x480 for Windows.
Ostensibly some people claim that they can change the resolution in the REDALERT.INI and get the resolution to change for the dos version.
I tried doing it with my version of Red Alert from the First Decade release, but I experienced some trouble with it not recognizing the dvd, so I can neither confirm or deny that it works. (Personally I suspect it doesn't, as I doubt that the dos version reads the .ini file.)
But if you want to try I've included it for you, if you want to give it a try.