ATI Radeon HD 4600, 4700, 4800, 5000, 60 series products are unaffected, as is Windows XP.
Update: ATI has released a Catalyst 12.4a driver hotfix for the affected cards.
Point the download save at the same directory as before The folder in question is your main game data folder.
If you have the game downloaded to D:\Games\Diablo-III-8370-en GB-Installer, please point the download to D:\Games\.
As has been mentioned, launching the Diablo 3 downloader and directing it to the same folder as before will allow it to download the installer files again.