Hello

I quote from http://www.devmaster.net/engines/
about 3dgs engine details

Artificial Intelligence Pathfinding, Decision Making, Finite State Machines, Scripted:

Where can I find a scripted FSM ?

a fsm is nothing but a simple robot. the guard model in the office level eg is a FSM (-->template scripts).

FSM are much more than just a simple robot. The whole AI in Quake, Doom, etc. are FSM's. So... it depends on how much code and time you invest in it.

BTW: you can do also a lot more things than enemy AI with FSMs. You can build NPC and Player - animation and -behavior on a unified FSM that is supported by one single animation-machine. Or you could even write GTA stuff with FSM just to control the traffic in the city. Whatever you have: different states of a NPC.. or of an object --> FSMs are the first thing you have to think of.

The best advice to start are flowcharts, etc. I suggest to read the general AI features over there at gamedev.net, there are some pretty cool articles about it.