Like fillip mentioned, bluetooth keyboards are not officially supported. You can enable the support for bluetooth keyboards by following the instructions at http://wiki.maemo.org/Fremantle_Unsu...tooth_profiles.

However, the keyboard layout uses the layout of the N900 build-in keyboard (e.g., you have to press 'shift + q' to type '1'). This makes it very annoying to use bluetooth keyboards. As far as I understand, this is because N900 is missing some layout files currently.

There is still hope that the layout support will get better some time in the future. Please vote here if you are interested in using bluetooth keyboards with N900: https://bugs.maemo.org/show_bug.cgi?id=6685