WTF?!
Two different subjects here i think: game resolution and DOSBox output resolution. It's difficult to explain but i'll try my best (; .
Game res: you can't "zoom in" or "zoom out" of a game unless it supports it. Most DOS games run at a fixed low resolution, thus you have a "small" image (=low number of pixels) compared to modern games which natively support high resolutions. Some DOS games support SVGA resolution(s), giving you a "larger" (=higher number of pixels) image. Not Wacraft 1/2 though IIRC.
DOSBox output: DOSBox can scale the game's image to whatever your hardware supports. This means the game image will still contain the original number of pixels, but DOSBox will stretch the image to fill your actual display. To configure this set "output=ddraw" or "output=opengl" in dosbox.conf and configure values for "fullresolution" and/or "windowresolution". If your display is not 4:3 set "aspect=true" and maybe play around with the "scaler" setting to see which scaling algorithm looks best to you.
This is probably too much info but I'm a big fan of the "teach them to fish instead of giving them fish" idea.