Create sections for "Home", "About Us", "Services" and all other parts of the website and then use a case statement in pagelayout.tpl to check the section and display the correct image name. You can get the section in your pagelayout.tpl through $DesignKeys:used.section
I hope this helps. I am also on my first ezpublish site.
Here's an easy way to work around your problem... use pagelayout.tpl for every page EXCEPT the home page and override it for the home page. The home page is node 2 by default.
You can also embed code in your pagelayout.tpl to display different images etc. in different sections of the site, like this: