If you are using VSTO SE to develop the Outlook 2007 Add-in. Visual Studio will add the setup project for you, you just need to add custom actions which grant full trust to your Add-in assembly into the Setup project. You can refer the following two articles:
If you are using Visual Studio 2008. You need to create a new setup project. But there are more things we need to take care of, like Registry and Manifest and Permission Trust, read more information in Mary Lee's article: