Download the AMD Catalyst 14.6 RC (14.200.1004.0 June 2) driver. This driver works with Windows 7 and 8.1.
We have a discussion thread open on this driver right here.
This driver originally supported only a few APUs and no desktop cards, now it has been modified to support desktop and mobile cards (you can check the supported card list in the forum post). So treat this driver as an unofficial one since it has been modified. The original driver can be found here.