make a "start.bat" in "hl2.exe" folder and try this, seems to work fine with my crap gfx card. Also modify textures from 32 to 16 bit in the option menu etc.
hl2 -condebug -mat_preloadshaders -preload -console -toconsole -dx8 -fullscreen -shaderdll shader_nvfx_ps20.dll -width 800 -height 600 +map d3_c17_13.bsp -heapsize 256000