CPU: AMD 1.86 Ghz Core 2 Duo 
RAM: 938 Mb 
OS: Ubuntu 9.04, i686
Video: GeForce 7025 / NVIDIA nForce 630a
I've searched and found several comments on Overture crashing, but they all seem to be related to specific moments in the game, like moving to a new level or going through a door.  Mine is different.  I can get about five to ten minutes into it and it crashes no matter where I am.  It has happened in that first room, in the snow banks where you have to pick up the rock, and in the underground storage room, which is as far as I've made it so far.  The game freezes, minimizes, and I lose all control of my mouse, even outside the game.  The only option is then to completely restart my computer manually.  
All of my drivers are up to date, I have the latest version of the game, and I've even tried the 
http://www.unbirthgame.com/Penumbra.zip fix per the forum, but I didn't have the Penumbra.exe within the folder that that post said I should replace, so that seemed to be a waste of my time.  
Here is what the hpl.log said--I hope maybe it really is something as simple as a missing image file like the error at the end might suggest.  I'm not well-versed in software, which might explain why I haven't found a solution yet, but I wouldn't have thought I would have to work so much on a program I paid for.  I expect a lot of glitches from 
free, open source stuff, but I want to play the game; it seems like it might be a lot of fun, so I'll give it a little more effort, I guess.
-------- THE HPL ENGINE LOG ------------
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 haptic module
 Creating scene module
--------------------------------------------------------
Initializing Resources Module
--------------------------------------------------------
 Creating resource managers
 Misc Creation
--------------------------------------------------------
Initializing Graphics Module
--------------------------------------------------------
 Init low level graphics
 Setting video mode: 1440 x 900 - 32 bpp
 Init Glee...OK
 Setting up OpenGL
  Max texture image units: 16
  Max texture coord units: 8
  Two sided stencil: 1
  Vertex Buffer Object: 1
  Anisotropic filtering: 1
  Max Anisotropic degree: 16
  Multisampling: 1
  Vertex Program: 1
  Fragment Program: 1
  NV Register Combiners: 1
  NV Register Combiners Stages: 8
  ATI Fragment Shader: 0
 Creating graphic systems
  Creating Renderer2D
  Renderer2D created
  Creating Renderer3D
   Load Renderer3D gpu programs:
    Extrude
CG: 'ShadowExtrude_vp.cg' using profile: 'vp40'
CG: 'ShadowExtrude_fp.cg' using profile: 'fp40'
    Diffuse Vertex
CG: 'Diffuse_Color_vp.cg' using profile: 'vp40'
    Diffuse Fragment
CG: 'Diffuse_Color_fp.cg' using profile: 'fp40'
    Fog
CG: 'Fog_Solid_vp.cg' using profile: 'vp40'
CG: 'Fog_Solid_fp.cg' using profile: 'fp40'
   Creating fog textures: Solid Additive Alpha 
CG: 'refract_vp.cg' using profile: 'vp40'
CG: 'refract_fp.cg' using profile: 'fp40'
CG: 'refract_special_fp.cg' using profile: 'fp40'
   init sky box
  Renderer3D created
 Creating screen buffers size 1440.000000 : 900.000000
 Creating programs
CG: 'PostEffect_Blur_vp.cg' using profile: 'vp40'
CG: 'PostEffect_Blur_Rect_fp.cg' using profile: 'fp40'
CG: 'PostEffect_Blur_2D_fp.cg' using profile: 'fp40'
CG: 'PostEffect_Bloom_vp.cg' using profile: 'vp40'
CG: 'PostEffect_Bloom_fp.cg' using profile: 'fp40'
CG: 'PostEffect_Motion_vp.cg' using profile: 'vp40'
CG: 'PostEffect_Motion_fp.cg' using profile: 'fp40'
CG: 'PostEffect_DoF_vp.cg' using profile: 'vp40'
CG: 'PostEffect_DoF_fp.cg' using profile: 'fp40'
  RendererPostEffects created
 Adding engine materials
--------------------------------------------------------
Initializing Sound Module
--------------------------------------------------------
 Initializing OpenAL.
  Trying to open audio device... Success!
  Device name: ALSA Software on default
  Number of mono sources: 32
  Vendor name: OpenAL Community
  Renderer: OpenAL Soft
  OpenAL Version Supported: 1.1
  EFX: 0
  Output Devices: 
    ALSA Software on default
    ALSA Software on HDA NVidia [ALC888 Analog]
    ALSA Software on HDA NVidia [ALC888 Digital]
    OSS Software
    Wave File Writer
--------------------------------------------------------
Initializing Game Module
--------------------------------------------------------
 Adding engine updates
 Initializing script functions
--------------------------------------------------------
User Initialization
--------------------------------------------------------
WARNING: Language entry 'EventKeyInNoPower' in category '01_10_small_shaft' already exists!
Initializing Penumbra: Overture
  Version	$Rev: 3013 $
  Date	$Date: 2010-02-06 22:45:08 +0000 $
Checking Supported Profiles
  Profile CG_PROFILE_VP20 is supported
  Profile CG_PROFILE_FP20 is supported
  Profile CG_PROFILE_VP30 is supported
  Profile CG_PROFILE_FP30 is supported
  Profile CG_PROFILE_VP40 is supported
  Profile CG_PROFILE_FP40 is supported
  Profile CG_PROFILE_ARBVP1 is supported
  Profile CG_PROFILE_ARBFP1 is supported
  Profile CG_PROFILE_GLSLV is supported
  Profile CG_PROFILE_GLSLF is supported
  Profile CG_PROFILE_GLSLC is supported
Trying to load vertex program!
CG: 'Test' using profile: 'vp40'
Success!
CG: 'DiffuseSpec_Light_vp.cg' using profile: 'vp40'
CG: 'DiffuseSpec_Light_Spot_vp.cg' using profile: 'vp40'
CG: 'BumpSpec_Light_fp.cg' using profile: 'fp40'
CG: 'BumpSpec_Light_Spot_fp.cg' using profile: 'fp40'
CG: 'Ambient_Color_fp.cg' using profile: 'fp40'
--------------------------------------------------------
Game Running
--------------------------------------------------------
Loading collada for 'maps/level01_02_mine_entrance.dae' took: 611 ms
CG: 'BumpColorSpec_Light_fp.cg' using profile: 'fp40'
CG: 'BumpColorSpec_Light_Spot_fp.cg' using profile: 'fp40'
CG: 'Fog_Trans_vp.cg' using profile: 'vp40'
CG: 'Fog_Trans_Alpha_fp.cg' using profile: 'fp40'
CG: 'Diffuse_Light_vp.cg' using profile: 'vp40'
CG: 'Diffuse_Light_Spot_vp.cg' using profile: 'vp40'
CG: 'Bump_Light_fp.cg' using profile: 'fp40'
CG: 'Bump_Light_Spot_fp.cg' using profile: 'fp40'
CG: 'Diffuse_Light_fp.cg' using profile: 'fp40'
CG: 'Diffuse_Light_Spot_fp.cg' using profile: 'fp40'
CG: 'Fog_Trans_Mod_fp.cg' using profile: 'fp40'
ERROR: Couldn't find particle system file 'particle_dust.ps'
ERROR: Couldn't create particle system 'sust01' of type 'particle_dust'
ERROR: Couldn't find particle system file 'dust_sust01.ps'
ERROR: Couldn't create particle system 'particle' of type 'dust_sust01'
ERROR: Couldn't load particle system 'particle' with type 'dust_sust01'