I recently updated my NC10 from lenny to squeeze. After that xbacklight stopped working:

$ xbacklight -set 50
No outputs have backlight property

Looks like the solution is to upgrade to the latest BIOS (11CA, available from samsungpc.com).

I created a FreeDOS USB stick with information available from Smörgåsbord and fdos.org, copied the BIOS to it, bootet from the stick and successfully flashed my NC10.

Now xbacklight works again.