This bug seems to be common with some of the newer samsung laptops such as the nc10, nc20, q210, q310 etc..
First you add an entry to /usr/share/hal/fdi/information/10freedesktop/30-keymap-misc.fdi to allow the nc20 key mapping to take place but then you get the problem where key release events are not generated for the brightness controls (fn button plus arrow up / arrow down).
I have already filed a bug with a patch to enable hal-info to recognise the keycodes for the nc20.
The other half of the fix is to stop the keys from repeating and I followed the example of other patches and tested a kernel that I compiled and it fixed the issue for me.
DistroRelease: Ubuntu 9.04
MachineType: SAMSUNG ELECTRONICS CO., LTD. NC20/NB20
Package: linux-image-2.6.28-11-generic 2.6.28-11.41
ProcCmdLine: root=UUID=09dc7cc6-6365-4e34-b5a5-d9fcb999ef3a ro quiet splash
ProcVersionSignature: Ubuntu 2.6.28-11.41-generic