I assume you are trying to add a domain name manually from your Windows Server 2008 server with IIS 7.x and all connections were already setup properly. All your clients can browse to your domain / IP but they were prompted for user name and password due to the permission was not setup properly.
Please follow steps below:
Create a web anonymous user
1. Log into the Server.
2. Right click on "My Computer" -> "Manage".
3. Expand the Server Manager:
Configuration -> Local Users and Groups -> Users.
4. Right Click on "User" -> "New User ...".
5. Enter a user name; example: domain.com_web.
6. Enter a password for domain.com_web.
7. Click "Create".
8. Close this console.
Assign Folder Permissions
1. Right click on your web folders -> "Properties".
2. Click on "security tab".
3. Click on "Edit" and select "Add".
4. Select the "domain.com_web" user you have just created and "Add", click "ok".
5. Allow permissions below:
- Read & Execute
- List Folder Contents (optional)
6. Click "Apply" and "Ok".
C) Add Virtual Directory / Domain in IIS
1. Open IIS console or run "inetmgr".
2. Expand the Local (server Name) and list down the Sites, Right Click on Sites -> Add Web Site.
3. Enter Site Name such as domain.com, Physical Path such as C:\Domains\domain\domain.com\wwwroot.
4. Click Select if you want to select a different application pool than the one listed in the Application Pool.
5. Enter the IP address to use for this web site, use port 80 and enter the hostname with your domain name such as domain.com then press OK.
6. Next, you will need to assign the web permission to your wwwroot path.
7. Go to your IIS 7.x -> Local(Server Name) -> Sites -> domain.com -> Authentication, check if Anonymous Authentication is enable, if not right click and enable it.
In command line, you may use the following command.
appcmd add site /name: string /id: uint /physicalPath: string /bindings: string
The variable name string is the name, and the variable id uint is the unsigned integer that you want to assign to the site. The variables name string and id uint are the only variables that are required when you add a site in Appcmd.exe.