cool this is what I did step by step.

1 - Remove ALL parings from PC and N900
2 - Open BlueMaemo
3 - click on wait for connection
4 - Open BT panel on my PC and search for device
5 - Select N900 start pair enter code etc.
6 - I think this is key step. WAIT for the PC to finish install all drivers.
7 - The N900 screen will suddenly chge to being connect to the PC via Maemo blue, and you get a nice screen with mouse keyboard etc

Hope this helps