I'll see if I can explain this decently.
You header, nav boxes, footer, top etcetera are each sliced.
Now they are place by using divs and CSS, if you need to learn those, I would recommend.
http://www.w3schools.com/
Or, if you don't want to learn, you could see if someone here would be willing to do it for you.
One way to get the content to expand is this.
Have the top, middle, and bottom section images sliced and declared as something like this
Code:
<div class="content">
<div class="contenttop">
</div>
<div class="contentmiddle">
Content Here
</div>
<div class="contentbottom">
</div>
</div>
Now, the <div class="content"> tag is the content "container" which keeps everything nice and organized, The top and bottom tags would include the image of the top and bottom of the content image.
The main thing is the content middle, which should have the middle section of the content image along with the ability to repeat-y in the css.
So an example of the css could look like this
Code:
div.content {
width:600px;
min-height:300px;
margin-left:auto;
margin-right:auto;
}
div.contenttop {
background: url(contenttop.png) no-repeat;
height:20px;
width:600px;
}
div.contentmiddle {
background: url(contentmiddle.png) repeat-y;
width:600px;
min-height:130px;
}
div.contentbottom {
background: url(contentbottom.png) no-repeat;
width:600px;
height:20px;
}
This is a way it COULD work, it could be different for you, buts a very reasonable way to expand the content area.