Basically:
I installed extmou and extkbd
rebooted
enabled bluetooth and went to "Devices"
Pressed "New" button.
I then pressed "reset" button under the Mediaboard
N900 should then show its fond the keyboard
Select the keyboard
press the "Pair" button
then type the number shown (on the N900) on the mediaboard and press enter
you should get a message that the pairing is complete
press the "save" button

Start the "settings" app and the "external keyboard" option should be shown and select it
Press the "Tools" button and press the "reconnect keyboard" button
You should see a message saying "..connected.."
at this point you should be able use the trackpad
If you get any error messages at this point (e.g. "host is down" or app seems to hang) then re-pair the keyboard and try again.

Those are the steps I take that seem to work.

However, in Maemo only the alphabet keys, enter, backapce and cursor keys work. All other keys are totally dead.

When I am using Easy Debian and use an applictions within it, all the keys work as expected - just like a standard keyboard.

I also keep the "External Keyboard" settings app open because sometimes the keyboard loses the connection and I have to use the "Tools" button to reconnect.