Ok, I Had same issues too.
This is how i fixed mine on my Intel Pentium Dual Core E2200
Check your bios in the cpu settings Deactivate/ Disable "Spread Spectrum" and "Intel Speedstep Tech" these 2 was causing my game to crash to desktop within 15 mins of play.
If that doesnt work Get the free app "WinLauncherXP" and set it so when you run Left4Dead it will only run on 1 core instead of both, although this will lower your game performance some it will allow you to play. i was using the WinLauncherXP method untill today when i fixed the issue properly.
Hope this helps
Ill Copy / Paste links to this post in the other similar crash to desktop threads so ppl can see it.