How to add a field in contact form?

Hello,

I want add an address field in the contact form.
(i tried to edit contact.php, but i'm not a programmer, i made a big mess of it, so i gave up)

All help is  appreciated.

Pieter

@pietkei
It's not just about adding field, following items must be considered/done:
- add field into form
- update controler for form processing to accept this field
- update email template to accept this field
- update email function to accept this field