I moved this to SecurityCenter as I assume we are talking about home user software which you have downloaded.
More information would help, such as your operating system and service pack and what version of Internet Explorer is installed.
(Whether or not you use IE as your default browser is irrelevent - McAfee and some other processes do use it).
Was the installation successful and have you tried rebooting to see if that helps?
What version of McAfee is installed? Open it and click 'About'.