inside the ZIP you got 2 folders, Materials and Models put them under the following folder (This folder will NOT exist by default!):
Steam\steamapps\common\Source SDK Base 2007\zpscustom
ZPS and Contagion is made by Monochrome LLC.
A friend of mine wanted me to port the Eugene to ZPS, and I did. I might also do Marcus later. I take no credits from the models except for porting it over to ZPS. The models itself and its textures is by Monochrome LLC, the same creators behind Zombie Panic! Source.
Have fun using it :)