1. And which Service Pack? SP2 is at least required.
  2. No, they don’t use different engines. But it’s important for the download link of latest program version. And there are different features in the versions.
  3. Anyway you should download the latest version 2014.9.0.2013: http://files.avast.com/iavs9x/avast_internet_security_setup.exe and latest removal tool: http://files.avast.com/iavs9x/avastclear.exe
  4. Some have other security software like Spybot Search&Destroy installed that can cause problems.
  5. Apology is accepted.

DJBone