Using text area for free shipping code

[squirrel]

I need to be able to enter a code in a text area of the checkout pages that would allow special clients to have free shipping (without belonging to a pricing group). I'm using the flat rate module.

I noted in other posts, although I can't seem to relocate them, that I can simply set flat rate shipping to false in the flat.php when certain conditions are met. I think I can handle that coding. What I can't seem to find is the form where I would place the text area. Also I'm not exactly sure how to access that posted variable.

Also, I think that someone mentioned that the admin side would have to be modded also. I'm not sure I understand where that would be done. Any help would be greatly appreciated.

Squirrel