Had a few people asking me how to get it to run, so I saw this on the battle.net by a guy called D1STORT3D
Inside the folder libraries/documents/diablo III there is a file named "d3prefs.txt". Open it.

Change:
- DisableTrilinearFiltering "1" (from 0 to 1)
- HardwareClass "1" (from 0 to 1)

Save the file and close it.
When you launch the game, you will still get the same “Unsupported graphics card” error that pops up. Press esc and the game will load.
Thought it was worth posting here

bare in mind it may have mixed results.