4
Never mind, found 'em. New to Xoops, Catads, PHP, MySQL and French, so it took a while. If it helps anyone else... I added new fields to the database and the following files:
modules/catads/admin/adsmod.php
modules/catads/adsitem.php
modules/catads/submit1.php
modules/catads/include/form3_ads.inc.php
modules/catads/include/functions.php
modules/catads/blocks/catads_myads.php
modules/catads/blocks/catads_new.php
modules/catads/class/ads.php
modules/catads/language/english/main.php
system admin/templates/catads_adsitem.html
system admin/templates/catads_myads.html
system admin/templates/catads_addsublist.html
system admin/templates/catads_item.html
I'm not using all of the pages, so you may need to change additional files, but it's a start.