Adding to the Shopping Cart [help (?)] popup

I would like to add an extra paragraph to the Shopping Cart [help (?)] popup.

I know that I need to add the new paragraph and heading to:
/includes/languages/english/CUSTOM/info_shopping_cart.php

But I've found two files which seem to be responsible for creating the popup:
/includes/templates/template_default/templates/tpl_info_shopping_cart_default.php
and
/includes/templates/template_default/info_shopping_cart/tpl_main_page.php

Which should I edit?
Where should I put the edited version?
What's the other one for?

Thanks
Alan

This one's the one that does the actual display:

AlanQ:

/includes/templates/template_default/info_shopping_cart/tpl_main_page.php

The other is ... well ... not used.

Thank you DrByte, that worked.

Does the existence of
/includes/templates/template_default/templates/tpl_info_shopping_cart_default.php
mean that there's some 'cleaning up' of the files that needs to be done?
Or is it there for some future use?

Alan

Without investigating further, I believe it's a need for cleanup, no future-use plans there as far as I recall at the moment.

The background of the (help (?)) is black. Where can I change that? What file and what area do I change from black to another color?

http://kitsandcaboodles.com/cart/index.php?main_page=shopping_cart

Thank you very much.

kits1:

The background of the (help (?)) is black. Where can I change that? What file and what area do I change from black to another color?

http://kitsandcaboodles.com/cart/index.php?main_page=shopping_cart

Thank you very much.

Hi Just wondering, does anyone have solution for this? The help link in shopping cart has black background, and the text is grey. CSS file actually has background-color: #ffffff. Any idea?
Thanks

sounds like you have custom template.... if that so , without link to your site , would be impossible to advice