<?php if($_SERVER['PHP_SELF']==index.php)

{echo "<p>This is the home page dude.</p>"; }
else
{echo "<p>This is NOT the home page dude.</p>"; }

?>

I have a php include that I only want to activate on certain pages and I though the $_SERVER['PHP_SELF'] might be the mechanism to do that.
Having some troubles though.

You're close:

PHP Code:

<?php

if($_SERVER['PHP_SELF'] == 'index.php')
     echo "Home Page";
else
     echo "Not Home Page";

?>

The only problem was that you forgot to surround index.php with quotes. Anything that is a string should be surrounded with quotes (in most cases). Notice that I also cleaned up your code a bit, I think a full script written in that style would be very difficult to read.

PHP Code:

<?php
if($_SERVER['PHP_SELF'] === 'index.php'){ // Notice the 3 = bits and the {
     echo 'Home Page'; // ' instead of " 
} else { // The brackets make it easier to debug.
     echo 'Not Home Page';
}
?>

Would be better.

Though, if you looking to confirm the right page has been included use this code (it's more easy to paste):
// Main file - Start

PHP Code:

define(INSCRIPT, "yes"); 


Anything being included

PHP Code:

if(INSCRIPT !== "yes"){
die('Sorry, you are accessing this page in the wrong way');
} 


IMO, not using {} brackets on if, else statements, etc, is a bad habit to get into, so I am in agreement with Mike here.

Thanks guys.

To be honest though, I`ve always been a bit confused about the necessity for using === as opposed to just ==.

Is there a strong argument for the former?

In this case it won't make a difference. === not only compares the values but also the type.

So 5 == '5' will return true but 5 === '5' won't
$_POST['username'] == '' will return true if the user did not enter his name, or if there is no such field as username

$_POST['username'] === '' will return true only if the user did not enter his name meaning the field must exist

In most cases == will work just like === but keep an eye out for the special cases when the type really matters.

In your case using === does not make any difference. I've read that === has better performance but it is negligible