Don't use frames or iframes. I say it over and over and over and ....
What you want is perfectly posible using div tags. The scrolling effect can be acheaved easilly by using the overflow:scroll or overflow:auto style in your css.
For example
Code:
<style type="text/css">
#header {
height:10%
}
#sectiona {
float:left;
width:30%;
height:90%;
overflow:auto;
}
#sectionb {
float:left;
width:70%;
height:90%;
overflow:auto;
}
</style>
<div id="header">
nav links however you want them
</div>
<div id="sectiona">
the content of section A
</div>
<div id="sectionb">
the content of section B
</div>