LEFT FOR DEAD ONLINE FIX AND LATEST PATCHES
These are auto installers, one click and start playing online.
You need to have L4D installed first though, I suggest Skulptura release.
First insatll Rev_Emu 9.6a, it let's you play online.
And then the co-responding patches.
In install in your L4D folder.
In install where you have your left4dead.exe
Google Skulpture L4D release, it's da best.