When you begin the Outlook 98 installation, you should be aware that any previous version of Outlook will be replaced. Another inescapable result of the Outlook 98 installation is that Internet Explorer 4.01 (or later version) will be installed replacing any previous versions of Microsoft Internet Explorer that you have on your computer. You don't have to use Internet Explorer 4.01 as your default Web browser, but it must be installed on the computer for Outlook to have full functionality.