Windows 7 Brightness & BIOS Issue

Hello,

Have a Dell D520 that I've installed W7 Pro on and it's all fine and performing well apart from one strange problem. I noticed that the brightness was a bit low once windows had started, I tried holding the fn key and pressing Page Up to increase the brightness but this did nothing, Page Down to decrease brightness also now does nothing (these keys worked fine with the previous XP install).

So I rebooted and went into the bios and noticed that the brightness level for when on battery had been taken down to about 6 out of 10 instead of the default (and the level that I want) of 10. I turned it back up to ten and everything looked better. Rebooted, stil bright when the glowing windows splash comes up but then as soon as the mouse pointer becomes available it goes dark again, back into the bios and the setting is back on 6!

How can something with the windows install (at a guess) be messing about with my bios brightness settings?

Thank you.


EDIT: Ok I was being stupid, Page Down and Up adjust the volume (was wondering why the music was so loud at some points...), it was the up and down buttons on the arrow keys that do the brightness, it works, my other dell has it the other way round, that's what threw me (excuse). Thing I still don't understand is how W7 is messing with the bios settings, they always used to stay the same no matter what the settings in the os were with XP, they would only change when you change them in the bios, anyway not a problem now.