I have tried the following:

- pincodes 0000, 1234, 9999, 00000000000000 on the N900

- Pairing the mouse to my Macbook running OS X 10.6; no go. It doesn't require me to enter a pin, but it fails to "connect" to the mouse even though it does discover it ok. No explanation for the failure is given.

- Pairing the mouse to Windows XP running inside VMWare on my Macbook, after having installed the Intellipoint software for Windows. I was given the option of "No passkey" and it paired and worked just fine.

The mouse is Microsoft Wireless Intellimouse Explorer for Bluetooth (phew!), which is, I believe, the first Bluetooth mouse Microsoft did.

By the way, the Microsoft support article posted was mostly related to using the mouse with the Microsoft-supplied Bluetooth transceiver, which I also happen to have but which is obviously not very useful with the N900.

Basically I think the problem is that it's microsoft.. I'll try to get another kind of BT mouse for loan from somewhere.