I had a post about this. No way to completely disable the backlight/screen saver?
See here please Answer Center | AT&T
The maximum idle timeout is 2 min, can go any higher. its more for presentations, etc where I want it to not go "idle" to screen saver.
Automatic dim back light doesnt solve, seems its something else.
Someone talked about changing security option value timeout, but didnt help.
I saw also some program thta costs 3 dollars that lets you control the backlight, not sure if it would help: BlackBerry App World - Screen Light