1. delete the bluetooth phone entry on your pc if it's already there
2. delete the bluetooth pc entry on your phone if it's already there
(so afterwards both devices shouldn't "know" each other ^^)
3. make sure that bluetooth on both devices is disabled
4. start bluemaemo on n900
5. click on "wait for connection"
6. activate bluetooth on your pc and search for devices
(n900 should be recognized as "other" or "hid" - not as phone afaik)
7. pair both devices
8. the "waiting for connection..." window on the n900 should disappear and it should show the bluemaemo menu
9. now it should work properly ^^
(10. if not - maybe restart your pc and try again)
(11. if step 10 doesn't help make steps 1 - 9 again... i had to do it several times too before it worked for me)