Not quite sure what the exact question is but...
You can use Dreamweaver to create the form and the thank you page (both can be plain html) BUT you will need a form handler to process the data from the form. That file must be php (or some other server-side language).
Form posts to form handler, form handler processes data and redirects client to thank you page.
You can use DW to code the PHP (and it does a nice job of color coding the PHP code for you) or you can use somethnig like Jack's Formmail.php http://www.dtheatre.com/scripts/ That script will email the contents of the form to an email you decide. You will have to download Jack's script and upload it to your server of course, and you will have to point your form at it, and tell it where your thank you page is. I also recommend implementing some form of spam blocker. I like formSpamBotBlocker by Giorgos Tsiledakis at http://datexp.com/linux/fsbb/ (it's in Russian, so run it through Google translate if you aren't fluent). I actually use a verson of both scripts that was integrated by RVSiteBuilder and I use it in my classes.