This is actually possible to do without any kind of addon. XP Pro will still allow multiple sites to run under IIS, but they have removed the option to configure this from the GUI. They have also removed the ability to have more than one site run simultaneously. Using the scripts found in the \Inetpub\Adminscripts directory you can add additional sites, and then use the IIS admin snapin to toggle which one runs.
Best Solution
No, it is not possible. The version of IIS is tied to a specific version of Windows.
More information available at http://support.microsoft.com/kb/224609.