Yea, Zombie servers just auto-DL on CS:S.
If you want to actually have a total mod, then Tiderman's post shows how.
If you want my advice, look for these things for a good zombie server:
:: Zombies can Push Obstacles quite easily.
:: Zombies have a "jetpack" function. (No really, its good

)
Also, zm_lila_panic_v2 is a very good map, if you can find it somewhere.
If you find a server with these things, please tell D= (the one I played on got taken down

).
Good Luck! :razz: