Traditionally IIS does not allow you to specify a hostname on a website that uses SSL. This is not completely true, it does if the friendly name of the certificate starts with a an asterisk, or if you use the command line. But if you don't want to do either you can use this tool, it's called IIS Buddy, it looks and feels like the IIS manager, a subset at least. It lets you configure the website site just as you would configure a site that doesn't use IIS. And it's free.