What other security software are you using? I am running Avast! 6 free with OA++ under Vista and also Avast! 6 AIS with a beta of OA++ under W7x64, with and without SP1 with no problems. What were you running before Avast! 5? Where does the boot hang? Have you tried removing all your USB connections before you boot?=Have seen that issue lately particularly with external USB2 drives.