Add content (from a file) to a file (html file) based on user selection of radiobuttons/checkboxes

Hi, I am working on creating a page, where the user can see an html editor page, with content from a file preloaded in the editor. The scenario is that suppose a section of html code is missing, the user can select from a list of radio buttons, A..B...C to determine which file is to be added in. I would think Ajax would do the trick, because I want to add this content in before the form is submitted. I will post the code that I have and explain which files need modification if there is a person who is interested in taking on the project. If you wish to look up info, I am using Xinha Editor tool if you want to take a look at that.