=INSTALLATION=
Just drop the materials folder in your left4dead directory.

Once extracted, open up pak01_dir and find these:

$baseTexture "models\survivors\namvet\bill_color"
$baseTexture "models\survivors\namvet\bill_head"

And change them to:

$baseTexture "models\survivors\namvet\bill_color2"
$baseTexture "models\survivors\namvet\bill_head2"

Enjoy :)