Did you install the Standalone Windows Vista Service Pack 1 and Windows Vista Service Pack 2 aswell as Microsoft Security Essentials and its Standalone Update before the system drivers in the correct order? If not reinstall the Operating System this way.
Although almost all official documentation mentions nothing about installing the Service Packs. Installing the Service Packs before the drivers increases performance greatly on some systems especially with Service pack 1 as it includes a lot of drivers and the drivers present in the service pack conflict with the drivers already installed on the system if the Service Pack is installed after the drivers. Installing the drivers after the service pack doesn't have the problem.
See Windows Reinstallation Guide / A Clean Install of Windows Vista for details.
P.S. what was the model of hard drive you installed?