Download AMD Catalyst 13.x (126.96.36.199 June 21) as provided by asder00. This is the Win 8.1 Preview driver now modified to work with Windows 7 and 8. Please consider this to be a beta driver.
Do not install any CAP with this, the one included is newer. ***Note for Windows 8 users only: To install and use this driver you must disable the Driver Signature Enforcement or enable the Test Mode.***