Just replying to your message on my post about custom header image issue. I have to say I am new to WordPress & it has taken me a little while to get the right coding to add my image header (in place of header text) and get it clickable. I sorted the clickable bit with code in my header.php so I guess you need to edit that to get yours clickable as a link to the relevant homepage.
Here is the relevant part of my header.php code that makes the image clickable. If you do something similar in your header.php you should get it working!
<a href="<?php bloginfo('url'); ?>">
<img src="http://learningthepianohelpsite.com/wp-content/uploads/2010/04/learningthepianohelpsite.jpeg" alt="<?php bloginfo('name'); ?>" />
<br /><br /><br /><br />
<?php bloginfo('description'); ?></p>
I hope this helps you (if it does or doesn't(!?) I would appreciate your feedback!). Goodluck and best wishes