Looking at the release notes:
Highlights of the ATI Catalyst™ 9.11 Windows release include:
GPU Acceleration of H.264 video content using Adobe Flash Player 10.1 Beta
This release of ATI Catalyst™ supports the new Hardware Acceleration features of Adobe Flash Player 10.1 Beta for video encoded in the H.264 format. Adobe Flash Player 10.1 Beta introduces hardware-based H.264 video decoding to deliver smooth video playback, reduce system resource utilization, and preserve battery life. Adobe Flash Player 10.1 Beta is expected to be available for download from Adobe Labs (labs.adobe.com) before the end of the year. This feature is supported on the ATI Radeon HD 5800, ATI Radeon HD 5700 and ATI Radeon HD 4000 Series of products
High Quality downscaling for video transcoding MSE
This release of ATI Catalyst™ includes an enhancement for the ATI Video converter for users transcoding high quality interlaced content (1920x1080i @60i videos) down to small resolution progressive content (320x240 @30p - iPod videos as an example), by maintaining high visual quality when down-scaling by a significant amount and converting interlaced video content to progressive.
Highlights of the Linux ATI Catalyst™ 9.11 release include:
Support for new Linux operating systems
- This release of ATI Catalyst™ Linux introduces support for the following new operating systems:
- RHEL 5.4 support
- openSUSE 11.2 early look support
AMD's chief marketing officer, Nigel Dessau, gives his (AMD-orientated) slant on the announcement here, and you can download the H.264-optimised Flash 10.1 beta here.
Anyway, here are the link to the drivers:
Cat 9.11 - Windows 7/Vista - 32-bit
Cat 9.11 - Windows 7/Vista - 64-bit
Cat 9.11 - Windows XP - 32-bit
Cat 9.11 - Windows XP - 64-bit
Full release notes here (PDF).