There are two ways of going about this:
1. You can simply link to whois.php and go into the script's admin panel and change the header / footer templates to reflect your site's header / footer. If you do it in this manner, then you will need to visit http://www.pwmhost.com/whois/whois.php in your browser and copy the HTML of the search bar to your front page.
(The above is the recommended method).
2. You can include it on your front page:
Place the following into your index.php page (http://www.pwmhost.com/index.php):
Code:
<?php include("whois/whois.php"); ?>
Then go into admin panel, and just clear the header / footer templates. You will also need to modify the Search Bar and Multiple TLD Page templates and change "[[site-url]]whois.php" to "index.php". There may be other similar replacements required as well.