Well, though I have connected my N900 to the internet trough my laptop a few times I'm using Windows 7 and a great program called Connectify (which unfortunately is for Win7 only). I can't guide you through the process since I don't know Vista but you need to share your internet connection also (you've probably done this). I suggest you first try to make a connection without authentication. And in further bad news there was at some point a thread around here about people not being able to connect their N900s over ad hoc with vista after the PR 1.2 update... If no one else can help then google is your only friend, I'm afraid. Good luck though.