[VBDev]

This is not so hard to understand as it user js, php and css.

You should dig in the code of my chatbox, in the following elements:

1. The $chatline_ondblclick in the mgc_chatbox.php file which shows the bit of code which is inserted in the tag where you want to be able to edit on double the content
2. The following functions in the mgc_chatbox.js file : inline_chat_edit (called on double click, it do the ajax sending), attente_recup_data_edit (waits for the returns of the ajax call), show_edit_chat (replace the current content by the input field), lancement_save_edit (called when the event onblur is fired by the input field, it manages the ajax call to save edited data), and finally attente_save_edit (waits for the return from the saved edited data ajax call).
3. The have a look in the mgc_chatbox.php file, the ajax_edit_getchat and ajax_save_edit DO which are the part called from the ajax.

This should help you a bit I think, but I can't spend time to explain you in details, time is preciou and I haven't that much (full timetable )