Simple Invoices - Forum

I found the solution here and was able to get it working using tecjam's solution: http://www.simpleinvoices.org/forum/discussion/comment/9108/#Comment_9108

However there is a drawback. When I create a quote it says "Due date: 7 July 2011etc" which is not applicable for a quote. Does anyone know if there is a way to nominate different templates for specific invoice groups such as a "quote template" for quotes, an "invoice template" for invoices etc? Could this be achieved maybe by making changes to the settings/preferences files or would it be better to use the same template for all invoice groups but edit the due date php code in the post above to something like "if preference_description value is equal to 'Invoice' then echo 'due date 7 July 2011' else do nothing" (sorry I can't write php code!).

Solution here: http://www.simpleinvoices.org/forum/discussion/comment/9164/#Comment_9164

pls explain to dummies:

tecjam's method.
1. after saving tecjam's code to si/templates/invoices/default/plugins/ folder as
function.due_date.php
or function_due_date.php

2. only add
{due_date date=$invoice.date days=14}
to templates.tpl and that is it.

it results in a blank page.
what

.

As dumnew suggested, please explain to dummies.