Is this possible to run it in window mode? Maybe some external tools to do it?
I recently got Disciples 1 working in windowed mode with 2x upscaling using DxWnd: https://sourceforge.net/projects/dxwnd/
Here is my DxWnd config file. Unzip the .dxw file and then import it into DxWnd using "File->Import...". You'll probably have to adjust the executable path. You might also need to clear your compatibility flags with "Tools->Clear Compatibility flags". Also, DxWnd options are rather unintuitive, so you'll have to spend time reading the in-app help file: just go to "Help->View help".
DxWnd config file: Disciples 1 (Windowed + 2x HQ UpScale).dxw.7z
DxWnd config file (faster bilinear interpolation): Disciples 1 (Windowed + 2x Faster).dxw.7z