fixed means that the columns do not resize with the size of the browser window. How the content appears from the index page to a single page depends upon the coding in each page.
The balanced news blog site is a fixed three column layout.
To get the three columns to be the same size, (ie., like the balanced news blog), you would change the "width" in each of the three divs.
If you placed this in the stylesheet:
#contentleft {
width:250px;
float:left;
}
#contentcenter {
width:250px;
float:left;
}
#contentright {
width:250px;
float:left;
}
your left sidebar would be
<div id="contentleft>
your center content (in the index page)
<div id="contentcenter>
and your right sidebar would be
<div id="contentright>
and in the index page, I think it would have to read
<?php get_left_sidebar() ?>
index stuff
<?php get_right_sidebar() ?>