Maybe... But I am having the exact same problem as you. In Win7 it does exactly what you described. The same laptop I have dual booting though and when I boot it to vista it connects to the iphone just fine and I can get on the internet. I don't know what to try next. I am thinking it is...
I upgraded to win 7 RC1 and now I can't connect to my iphone via ad hoc. Worked fine with the beta version, but now the phone connects to the ad hoc network but PC shows no connections.
I am dual booting with vista and in vista it works fine as well.
Any help is greatly appreciated.