Module extension of order

[cpuin]

Hi Everybody,

I want to create simple module extension of the order in the back-office.

When review the order that customer has placed I want to add some additional fields above.In these fields I will put some references.

After that I want to add above the order a button.When the button is clicked all information about this order: items, description, quantities, prices, address and my additional fields included will generate an XML which will be uploaded on FTP. I have the code I'm using on Codeigniter platform. What I need is the structure of the module, because I'm not aware where to put my code and how to add this GUI to the order hook.

Thank you in advance!