To check if your site is currently using PHP, simply go to a sub page on your site (contact page, buyer page, seller page etc.). Look at the address bar at the top of the page. If the last three characters of the URL are php then you will want to use the PHP paste on the previous page. For example: http://www.corpuschristihomes.net/sinton-real-estate.php
If not, you will want to use the HTML paste. Simply press the back button at the top of the page.