Firstly, always chose to do a “CUSTOM” Installation. That way you can chose what you want to install and not install.
Secondly, I suggest reading here>http://forum.avast.com/index.php?board=63.0
There are numerous topics and comments/information that may assist you.
Personally, I suggest you read as much as possible and make sure you fully understand what Grimefighter does and is it reliable. 