Display dims before sleep, no matter the setting

My MacBook will dim its screen (ie: reduce brightness) after about 10 seconds of idle time. I've read to stop this you need to uncheck the "dim display before sleep" checkbox under energy saver preferences. I've done this for both the power adapter and batery settings, but the display still dims! It will dim when running from the batery or the power adapter. It makes watching DVD's useless.
Has anyone else seen this? I find it annoying, but it's driving my wife crazy.
PowerMac G4 Quicksilver 867mhz, MacBook 2GHz (white)   Mac OS X (10.4.6)  


One option to try would be to change the login settings so that you are not automatically logged in when you start up to the computer. After you make this change, log out, log back in, toggle that display sleep setting on then back off and check the result.
Something else that might be worth a try...
First, I'm not sure what preferences, if any, will need to be reset after this. Also, I have not done this and do not know the result. As always, backup your stuff.
1. Go to the folder ./Library/Preferences/SystemConfiguration (not your Library folder but the one at the root level of your hard disk).
2. Drag the file named com.apple.PowerManagement.plist to the trash. You will be prompted to enter your admin password when you do this.
3. Restart.
MacBook/2.0/1GB/CTO (white); PowerBook G4 12/1.33   Mac OS X (10.4.6)   Airport Express, iPod mini, iPod nano