ATI has released a new driver and Catalyst Control Center software package for all flavors of Windows XP and Vista. There are a number of bug fixes incorporated into this release for both XP and Vista users and some performance tweaks as well.
"Performance Improvements: Half-Life 2: Episode 1 and Dark Messiah of Might and Magic performance improves on the ATI Radeon HD2900 XT Crossfire configurations. Improvements of 16% or more can be seen with HDR enabled."
Early reports also claim nice OpenGL performance improvement in Windows Vista as well. You can grab the drivers right here.