If you check out:
http://wiki.eqemulator.org/p?NPC_Models
you can see that the npc models are loaded from the _chr.txt file - think of it a global loading dock for models - not all zones support all models by default.
you need to get this text file to your players.
You can also see a handy generator linked from the same page here:
http://eoc.akkadius.com/AC/eoc/min.p...&GenRaceFile=1