Finally got this working with 2 separate machines, Windows Vista and Windows 7. After reading through the last 18 months worth of posts in this thread, the most useful information from multiple posters was to make sure that you did a fresh pairing with the N900 and PC prior to starting up BlueMaemo. Then, when you start BlueMaemo, you double click on the N900 device in your PCs Bluetooth Device Settings page, and enable HID profile, hit apply, and Windows installs the N900 as a Bluetooth keyboard as well.

One bug which I haven't seen posted is that if you start BlueMaemo without enabling Bluetooth, although it starts it changes the visibility of your N900 to hidden, even though when you go to settings, the tick box for Visible is still on. Further, I have not once been able get BlueMaemo working unless I enable Bluetooth first.

Lovely app, seems that development has stalled, I wish I could help in that regard. I would love to have a Windows Media Centre profile so that I could map different actions to different buttons.