Multiplayer HL2 level with NPC's ?

I was wondering how you would make a Multiplayer HL2 Engine map with NPC’s in it. (I guess my question is: Would this be a HL2 mod, or HL2:DM mod. And if so, how would I go about doing it ?)

Hope my wording isn’t too confusing. Thanks for all the help.

it took 5 seconds on google to find this:

unless you mean making a mod, in which case use HL2:DM because it has all the multiplayer networking done.

Thanks. More for putting up with users like me knack for not using Google than the actual question. You are a good person.