I can think of two ways to do this.
1) Spawn the entity in location, when the player is in the trigger zone.
There is already a script that you can use that comes with FPSC. In the Main Script choice for the trigger zone, set it to plrinszoneactivateused.fpi (or something like that). Then, set the name of the entity in the if used box of the trigger zone.
Then, the last step is to edit the entity 'Spawn at Start" field to No.
2) Using a script
When the player is in the trigger zone, the entity becomes active, much like a remote door.
Script for trigger zone: plrinzoneactivateused.fpi
(comes packaged with FPSC)
Script for the entity:
You'll have to some work by yourself, or post the main script for the entity and get someone to edit it for you. Anyway heres the state script you must put at the start of the main script.
:state=0,activated=1:state=1
It might look something like this.
Based on the default FPSC follow.fpi
;Artificial Intelligence Script
;Header
desc = Waits until activated by another objects If Used field, then follows waypoints
;Triggers
:waypointstate=0,activated=1:animate=2,waypointstart
:waypointstate=3:animate=2,waypointnext
:waypointstate=4:animate=2,waypointrandom
:waypointstate=5:animate=2,waypointreverse
;End of Script
Hope that helped,
JRH