Maybe this will help:
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To run Windowed: -sw -startwindowed -window -windowed
For ATI Cards: Run the exe with options -console -dx9 -width 1024 -height 768 -fullscreen
(Providing you have directx9 installed, otherwise replace -dx9 with -dx8)
For Nvidia Cards: -console -dxlevel 90 -shaderdll shader_nvfx_ps20.dll -width 1024 -height 768 -fullscreen
For standard dx9 codepath: -console -dxlevel 90 -width 1024 -height 768 -fullscreen
(unsure what this relates to, stick to the ones above)
You may want to add -heapsize 128000 or 256000 -- the game seems to use a default heapsize of 40 megs.
This is the amount of memory that will be reserved for hl2 in kilobytes.
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Hope this helps!
:-D