The IIS Express Web Server Not Installed dialog box appears when IIS Express is not installed on your computer and you open a Web site or application project that is configured to use IIS Express. You can choose to open the site in the local IIS Web server, download the components for IIS Express, or not load the site.
Select this option to open the Web site on your local computer by using the IIS feature in Windows 7, or the Web Server (IIS) Role in Windows Server 2008. This option applies only when you have the IIS feature or Web Server role installed.
Download the missing Web components (site is not opened)
Select this option to download and install the components for IIS Express. After the components have been installed, you will be able to open the site in IIS Express.
Leave the site unloaded
Select this option if you do not want to load the Web site or application.