Am I understanding correctly that those are to populate the settings on my Mac (rather than somewhere on the n900)? I've gone to Preferences>Network>click on "Bluetooth DUN N900" in the left hand pane, then in the settings on the right hand side I've put in what you say above (although it says "Account Name" rather than "Username". Still doesn't work I'm afraid. I think those might be settings for some other network ("Rogers" whatever that is?), from reading the link you gave.