Hi,
I see that Diablo 2 is not compatible with Windows Vista; you can check it by yourself, the link to have a check on that is given below.
http://www.microsoft.com/windows/compatibility/windows-vista/Search.aspx?type=Software&s=Diablo%202
However you can try to install the game in the compatibility mode. Refer the link below for more information on that.
Right click on the setup file>Click on properties>Compatibility>Place a check against “Run this program compatibility mode for” and select the previous version of Windows and install the game.
Make older programs run in this version of Windows
http://windows.microsoft.com/en-US/windows-vista/Make-older-programs-run-in-this-version-of-Windows
Also get in touch with the game publishers for more help on your issue.
Let us know if this helps
Regards
Sreekanth.