Change image every set seconds, plus back and forth buttons?

[keavon]

Hello. What I need is very simple in concept, although I am the worst in the world (not really) at JavaScript. I basically want to make a displayed image change, no special effects, every set amount of seconds. I also want to have a forward and backward image button to let you immediately switch while still continuing the timed changing.
I would really love some help!
P.S. It would be helpful to have an external script to shorten my page's code.

THANKS!
-Keavon