Zombie Panic Source is a SteamWorks supported mod, so this update should be delivered to you without any hassle via Steam. Changes to this new version include:
Added new ZP:S Barricading System
Added the ability to unload weapons
Added Punker player model and zombie counterpart
Added ZPO_Harvest
Updated Waitress rigging and textures
Updated ZPS_Cinema with new props, textures, and layout
Added weapon: Winchester Double barrelled shotgun
Added new hands for every player model and replacing old
Added new anims for every weapon (including the new Weapon)
Added infection notice on scoreboard for Zombies
Worth noting firing speed for Super Shorty is now faster
Added a massive list of prop models and materials
Humans now show bright green for zombies if infected (without Zvision)
Some great looking new maps included in this release as well as a barricading system which looks really impressive and should add a new dimension to the gameplay. Zombie Panic Source website.