creating e-mail newsletters is quite complicated, if you want to do it properly. Even if you are good in creating websites with Dreamweaver, you may run into all sorts of problems when trying to create and send mailings. Apart from the design and coding itself, which should work in all e-mail clients and text readers you will want to manage your e-mail list, unsubcribes and bounces. You will probably also want to know who opened your e-mail and who clicked which link. Your best bet would be to use a service like http://www.mailchimp.com/ or http://www.campaignmonitor.com/
For the design you can use the free e-mail templates they offer, and change them using DW4 to suit your needs.
For sending your mailing and managing your mailinglist they will charge you a minimal amount of money, which is well spent considering what benefits they offer. You can try it out for free.
As far as your code is concerned, for e-mail newsletters you are better of using a table based layout to be sure your layout remains intact in all the diferent e-mail clients. Find some advice here: http://www.mailchimp.com/articles/how_to_code_html_emails/
Keep it very simple. Add a prominent URL near the top of your email that leads to web page version of the newsletter for email clients that don't support HTML or Images.
Also read this. It has some good pointers and links to help you.