How helpful is it to use Dreamweaver for building internet sites?

extremely useful and great for beginners

Dreamweaver can be used by a new user as well as an advanced user for designing and coding of web pages.
It is fairly easy to understand the software and a lot of tutorials are available, the software itself has a lot of built in templates and functions for new users.
Moreover it is a dynamic software which can be used to code Javascript, XML, PHP and other client-server side languages.
Once you get used to it, it will be fun to design websites with this software.