This is a simple code to get all the 'bad words', stored in a database, out of the text. You could use str_ireplace but since that's installed on PHP5 only, this works as well. It strtolowers the text first then places capitals with ucfirst() where it thinks a capital should be placed, at a new sentence. The previous sentence is ended by '. ' then.

<?php
function filter($text){
    $filters=mysql_query("SELECT word,result FROM filter");
    while($filter=mysql_fetch_array($filters)){
        $text=str_replace($filter[word],$filter[result],strtolower($text));
        $parts=explode(". ",$text);
        for($i=0;$i<count($parts);$i++){
            $parts[$i]=ucfirst($parts[$i]);
        }
        $text=implode(". ",$parts);
    }
    return $text;
}
?>