trem reads all pk3's in the base folder, so it will find the model so long as u dont move it to a different location. but when you put it in radient u must make sure that you make a new folder in your base folder. move all related files, texutes etc etc
for example the niveus computer:
open niveus.pk3, find the files and put them in
C:\Program Files\Tremulous\base\models\mapobjects\niveus
for the rilfe model
C:\Program Files\Tremulous\base\models\mapobjects\rifle
so on a so forth.
soz if i dont make any sence,