Specify previous versions of Microsoft Office applications to keep or remove. This option is recognized by Setup only when you first install Office on a user's computer.
By default, Setup removes all previous versions of Office applications. To keep an installed Office application, select Remove the following earlier versions of Microsoft Office applications, select the Office application that you do not want to remove, click Details, and then clear the check box.
Note  Office Outlook 2007 cannot coexist with previous versions of Outlook. If you choose to keep previous versions, do not install Office Outlook 2007.