<pre>
<?php
$string = '<p>"Hello I am a hello".</p> <div style="border: 1px solid #000">Hello don\'t you think think</div>';

$string = preg_replace("/<([^>]+)>/i", '', $string); //Delete all tags in the string
$results = array(); //Initialize an array to hold our results
while(preg_match('/(\b[a-z\']+\b)/i', $string, $matches)) //While we can match any words with a-z or a ' in them do the following ($matches holds the item we have matched)
{    $string = preg_replace("/\b{$matches[0]}\b/i", '', $string, -1, $count); //Remove any instances of the word we just matched, so we don;t keep continually matching the same word. $count holds how many replacements of the word occur.
    $results[$matches[0]] = $count; //Update the results array so the key is the word matched and the value is the amount of times that word occured
}
print_r($results); //Print the results

?>
</pre>

$string = strip_tags($string); // Remove all HTML tags from the text. Assuming the markup is valid, this will get everything

// Now, to avoid getting words bundled in with punctuation, remove all punctuation -- with the exception of hyphens or your list of characters

$string = preg_replace('/[^\w\-]+/im', $string);

// Get an array of all words

$string = preg_split('/[\s]+/', $string); // Use preg split in case there are multiple spaces between some words

// Start counting
$counts = array()
foreach($string as $key => $word):
    if (empty($string[$word]))
        $counts[$word] = 1;
    else
        $counts[$word]++;
endforeach;

unset($string);

echo '<pre>';
print_r($counts);
echo '</pre>';

eval($string);