How do i do this? Counterstrike/Half life question?

ok you know in Half life when you play the campaign and when your on a certain mission that you can like add a monster? like lets say your in a part where there is zombies and then you can go into the console and type in give_monster zombie ETC and it'll spawn? well is there anyway i can create a server on LAN and add zombies, gargantua's, and others etc? if you type in give monster_gargantua for example it will say: Host_Error: PF_precache_model_I: 'models/garg.mdl' Precache can only be done in spawn functions." How do i fix this? also, is there anyway i cana dd bots to counterstrike 1.6? THANKS 10 points 4 answer