Problem with my iBook Leopard software?

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This is probably going to sound really stupid... it's because I don't know hardly anything about my computer.

I have a G4 iBook (yes, the crappy white one but with G4, whatever that means). It says OS X 10.5.2. I think I have Leopard. I'm using Safari. I want to turn off the automatic dimming feature. I already went to the apple the the upper left corner and went to system preferences and went to desktop/screen saver and put "never" for the screen saver.

I also went to the Safari tab in the upper left corner, went to preferences looking for how to turn off the dimmer... but I can't find it.

I was under the impression each program had to be told not to dim (?)

How do I make the computer stop dimming when I don't touch it (I'm trying to watch some South Park episodes with Safari!!)? Thanks a lot.