Firstly (and I speak from experience), stop using Dreamweaver. WYSIWYG editors do you no favors in terms of web development, and generally lead to unmaintainable, dirty code. You're better off writing HTML/CSS by hand and testing in your target browsers (FireFox, Chrome, IE etc).
Here is some code that will give you two fluid divs, side by side:
HTML
<div class="row">
<!-- .row > div is applied here because this div is an immediate child of the parent-->
<div class="first">
<p>First fluid section</p>
</div>
<!-- .row > div is applied here because this div is an immediate child of the parent-->
<div class="second">
<p>Second fluid section</p>
</div>
</div>
CSS
/* Apply this style to the parent div */
.row {
display: block;
width: 100%;
}
/* Apply this style to the immediate div children of the parent */
.row > div {
float: left;
display: inline-block;
width: 50%;
}
.first {
background: #FF0000;
}
.second {
background: #0000FF;
}
jsFiddle: http://jsfiddle.net/q9JpH/
Make sure you test thoroughly and apply graceful degradation where necessary...compatibility in the browser world is savage!