I had the same problem on a brand new Dell Inspiron 1764 laptop with Windows 7. After uninstalling McAfee and installing Avast, the Control Panel started to hang the entire Windows Explorer desktop. In addition, HP printer drivers failed to load, the Microsoft Teredo Tunneling Adapter reported uncorrectable errors, local area networking destabilized and there were numerous other crashes.
On a new Sony laptop with Windows 7 and an identical set of software applications including Avast, no similar problems occurred; Avast is smooth, stable and reliable.
Dell no longer provides free warranty support for software problems; software support is now a separate fee-based service. So I returned the Inspiron and got my money back.
Does anybody have additional information on the Control Panel related hangs? Is it only on Dell machines?