"After installing the game on a Windows Vista system and trying to run it for the first time, you are likely to get a message similar to:
This program has known compatibility issues
To fix this please patch the game using the latest patch. You can download and run the stand-alone patch from our patches page at Blizzard Entertainment - Patch Page. You will only need the latest full patch for the game. This will contain all previous information from previous patch updates.
The games will only work correctly when run with an administrator account. To do this with Vista, please Right-click on the game icon and then select Run As Administrator from the pop-up menu that appears. This will allow the game to run in Administrator mode.
If that does not allow you to run the game, please make sure you set the game to Windows XP SP 2 compatibility mode.
1. Right click on the Game icon.
2. Select "Properties"
3. Click on the "Compatibility" tab
4. Select "Windows XP SP2"
5. Click "OK"
Taken from Blizzard Support
Now when you have done all this crap try to launch the game. When I am lauching the game a little black thingy pops up in the left corner, this thingy needs to go trough all symbols you can press on a keyboard this might take 1 - 3 mins, but now you can also play diablo on vista
btw. screenshot;