You first need to convert the left for dead skin to a .smd file. Search for that on google.
Once you have the .smd, decompile a player model of counter-strike 1.6. Open up the .qc file and search for something like this
Code:
//reference mesh(es)
$body "studio"
There will be an extra quote after the "studio" and in between, the name of a reference. Search for the .smd of that reference.
Import it to milkshape, leave only "Skeleton" checked. Now import the l4d2 .smd with only "Triangles" checked, assign the bones and compile the model. That's pretty much it.
Everything is on google, just search.
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