you don't need to be a skinner to do it

you simply download valve's Half-Life model viewer (free to download) and open up the heavy.mdl in the player folder of models in the NS file.You go to texture,export the skin(s) and open the skins up in a photo editing program (except MSpaint,you can get a trial of photoshop for free for 30 days) and edit the picture as black&white,or as a grey scale.Import the skin back in,save the model,look! a new black and white skin for your model.