If the captcha code is not appearing on the page, then the GD Library is not enabled on your PHP server.
See the "How to enable the GD Library on your Testing Server" tutorial in the how to section of the contact form solution pack support page:
contact-form/
are the contact form files at the root of Dreamweaver Site you are using?
To be able to edit the server behaviors, the files will need to be extracted to the root of your site, if they are extracted to a subfolder of your site, it will not work.