Assuming you have a DNS server somewhere pointing an url to your machine, all you have to do is add a header definition to the site in question. In IIS, right click the site you wish to edit, then click "Bindings". You will see a dialog with various names and associated ports. Click "Add" to include a new definition. This is how name-based hosting works, and how IIS knows which "site" it should serve, based on the incoming request.