Can't change brightness on Dell Studio 1749

[Ustun Kaya <uskaya@gmail.com>]

Hello folks,

I installed Debian Squeeze on Dell Studio 1749 and I can't change the
brightness when the OS is up (Fn + F4 - F5 doesn't work). It works
when the BIOS screen is open, before booting into Debian. xbacklight
gives the following output:

ustun@Earth:~$ xbacklight -get
No outputs have backlight property

Any help?

Best,
Ustun