Combine 2 joomla template

Hi, I want to combine a joomla(2.5) template structure(rocketheme) with a joomla(1.5) template look and design. The structure MUST remain completely available for further modification and I want a garantee, completely functionnal with FF, chrome, safari, Internet Explorer, iphones and Android. Short description; put the menu and background images on another template. I have the template files for both for them. Home page, I want to have the same look as the attached image; new-look-home-page, menu and background image. Other pages, I want my site to show like the attached image; other-pages, only background image and menu. I want to have the background images linked to the main menu items. So I can create a new menu item and be able to link a background image on it, preferably by using the Gantry system if possible. Important; I want to keep the color chooser system. If you can show me something similar that you have done, it will be great. Thanks, Robert