I turned up all my graphics in the game to everything HIGH it plays very smooth but it has these fuzzys all over the screen like a old film.. I also want to note i play crysis on everything HIGH it has no problem's, here are my DXDIAG settings for my PC hopefully this might help.

I also installed a new graphics card on my computer its pretty big and i am a little worried about the over heating..but not sure if that is a problem i have a fan on the graphics card and the normal ones..but it seems like my power might not be enough for this graphics card. Im not sure.

Hi there,It's most likely the game engine not being very good, it's 5 years old and has been re-used from Half Life 2.
I don't think you've got any kind of heating or power issues there, so can you try updating L4D and the video card drivers.
ATI Radeon HD 4850 Series - Driver Download - PC Pitstop Libraries

I don't think it'll help.

Ok. it does tell me when i start the game in steam that i should update drivers thats what im currently doing its just a long download. And my O/S is 64 Bit does that mean i SHOULD download the 64 version?