Here's a short guide on opening DMG files on Windows and extracting data from them.
Download DMG Extractor (it's free).
Once installed, DMG Extractor will run automatically.
Open DMG Extractor and select the DMG file you want to extract
Click the "Open" menu icon on the top-left of the window.
If the DMG archive is password protected, DMG Extractor will prompt you for its password:
DMG Extractor will load the file you selected. If you have a large DMG file, a progress bar will show until the DMG file is loaded.
Now you should be able to see all the files contained within the DMG file and navigate folders and files.
Extract the files you want
Click "Extract", next to the "Open" button. You can choose whether to extract the whole of the DMG's contents into the same folder, or into a specific one chosen by you. If you don't need to extract all the files, just select the files you want and on the "Extract" menu click "Selected files to…"
That's it: extraction complete! Your selected files should now have been converted from the DMG file and saved onto your Windows computer ready for you to use.