For those that have purchased the full version there is now a patch to correct issues in all previous releases.  This include ATI HD graphics issues and Sound issues.
ChangeLog
2008-04-25 - Penumbra Overture V 1.0.2553
- Synced up to Windows 1.0.3 Patch
 
- switched to OpenAL Soft implementation of openal
 
- Fixed numerous shader issues on ATI and Nvidia cards
 
- support for ATI HD series cards
 
- Fixed various crashes in the game (especially when changing levels)
 
- Upgraded to Cg 2.0
 
2007-06-21 - Penumbra Overture EP1 V 1.0.679
- Synced up to Windows 1.0.1 Patch
 
- Fix sound related lockups
 
- Add list of "supported" Cg Profiles to hpl.log
 
- Added CG Profile overrides in settings.cfg (See default_settings.cfg)
 
- Unlock the mouse when in windowed mode AND in the menu
 
2007-05-28 - Penumbra Overture EP1 v 1.0.596
- Fix slow FPS in Refinery
 
- Fix missing steam in Refinery
 
- Add Version/build to hpl.log to identify installed version
 
Get the patch here 
http://support.frictionalgames.com/entry/65/