According to Rage3D.net ATI should have the new Catalyst 5.8 Radeon video card drivers on their driver download site on Wednesday, August 17th.
If you can’t wait an entire day, Driver Heaven has apparently scored a 24 hour exclusive on downloads, meaning that they’re available today. However, ATI notes that they will not give technical support to any drivers not downloaded through their own website, so you may want to wait until tomorrow.
For those currently testing Microsoft’s Windows Vista beta, ATI now has official beta drivers as well.