You're really asking someone to teach you to program. The skills and
techniques you'd use to turn your idea of how an NPC should behave into
Inform code are the same skills and techniques you'd use to turn any
idea of how a progam should behave into an algorithm. If you can write
code in any programming language, you shouldn't have much difficulty
writing Inform code.
If you are having problems coding something in Inform, then feel free to
ask a specific question and I expect the readers of rec.arts.int-fiction
will be glad to help you.
-- Gareth Rees In search of: revision-tracking software for MS Word documents.