I have the same problem.
AMD 3000+, 1GB RAM, ATI 9600PRO
I tried a demo version of the latest ATI Catalyst driver, and Omega drivers.
ATI: "Amnesia.exe caused an EXCEPTION_ACCESS_VIOLATION in module atioglxx.dll"
Omega: "Renderer 0 cound not be initialized!"
Try reinstall driver many times, and I looked for troubleshooting guide, but it did not help.
Penumbra series is working fine.
MainDemo/hpl.log:
"Version 1.10
-------- THE HPL ENGINE LOG ------------
Engine build ID 20100818114615
Creating Engine Modules
--------------------------------------------------------
Creating graphics module
Creating system module
Creating resource module
Creating input module
Creating sound module
Creating physics module
Creating ai module
Creating gui module
Creating generate module
Creating haptic module
Creating scene module
--------------------------------------------------------
Initializing Resources Module
--------------------------------------------------------
Creating loader handlers
Creating resource managers
Adding loaders to handlers
--------------------------------------------------------
Initializing Graphics Module
--------------------------------------------------------
Init lowlevel graphics: 1024x768 bpp:32 fs:0 ms:0 gpufmt:2 cap:'Amnesia - The Dark Descent - Loading...' pos:(-1x-1)
Setting video mode: 1024 x 768 - 32 bpp"