The image will, obviously, be resized as you change resolutions, maybe post a screenshot of what you get and what you suppose should be.

Meanwhile I've tried to run a Windows 3.1, because a friend of mine said it's working great for him. (I know that DosBox is for games, but he said it runs perfectly.) And yes, it is really working, but the previous problem stayed: if I give win a program as a parameter (win myprg.exe), it will open, but I can't see the top and the bottom of the program's window, because it's out of DosBox's window. (My friend managed DosBox to show the program correctly, but can't help me. When he starts win with the parameter myprg.exe, his DosBox windows is being resized, but e.g. the size of the characters or icons stays, so he can see the top and the bottom of the longer windows of the prg. We tried to use his .conf file on my machine, but it doesn't work either. However, it's not so surprising, because he has other video card and better monitor. But his example shows, that DosBox can do what I want, so I hope it will be working soon.) I don't know, maybe it's not about resolution, I'm not so familiar with these stuff. I hope this way it's more understandable, so that you can help me...

Thanks a lot:
akkkarki

Ahh I seem to get it...try changing Windows' 3.1 resolution inside DosBox and make sure you follow this guide:
Windows 3.1x DOSBox Guide