I have Windows 8.1 updated fully as of this date.
I had the same problem described above and d2vidtst was not working but I did get it to work. Here is how...
1. Follow everything Warblade said.
Right click on Diablo 2 shortcut under Compatibility tab check Run this program in compatibility mode for Window xp service pack 2; Check disable visual theme; Check disable desktop composition; Check disable display scaling on high DPI setting; check run this program as an Administrator.
2. Right click on D2VidTst
3. Click 'Troubleshoot Compatibility'
4. When the box comes up click 'Try Recommended Settings'
5. It should then pop up again saying you should run D2VidTst in compatibility mode with Windows Vista (Service Pack 2). Click on 'Test the program...'
6. Another pop up comes up. Click on 'Run Test'. The screen with run through a few things testing out your graphics card and drivers. Let it run its course.
7. Then it will have a pop up describing your video card and options to choose. Make sure the best one is checked, preferably one that says 'Direct3D' and not' DirectDraw 2D' and click 'Ok'.
8. Then it will ask 'Troubleshooting is completed. Is the problem fixed?'. Click 'Yes, save these settings for this program'.
9. You have finished. It should tell you its fixed and good to go. Click 'Close' or 'Close the Troubleshooter'
10. Run Diablo 2 and have a blast.