Template Problems

Hi, I have 3 domains: www.example1.com, www.example2.com www.template.com I have a PHP website on www.template.com with a database. in this database I have many tables one of which is sites, which has a list of the sites using the template with a site_id. Example of this data is:

Site_id,      URL,                                  Name
1               www.example1.com            Example 1
2               www.example2.com            Example 2

All of the other tables have the site_id in to relate to what site should be shown what information. However I can't have the user seeing the url as "www.template.com" instead it needs to say what they typed in for example "www.example1.com" I need to somehow redirect the user from "www.example1.com" (but mask the url) to "www.template.com" with the correct site_id passed through for every single page they visit (which says what data the template should load) which I would manually set in example1.com, this would then allow the user to browse the site and goto the next one when they want. Can anyone help???? Thanks