I just spent the past week looking for a good PHP FAQ script. They were all either too bloated with complicated features I didn't want, or too simple. The only one I liked was whatdafaq from http://www.pinkgoblin.com/
It does have an admin section where you can create/update/edit/rearrange FAQs.
Quite hideous, but easily edited to look quite nice. I can PM you the URL of my installation if you like.