From a tutorial for the Associate Theme from StudioPress: http://www.carriedils.com/customize-the-homepage-for-the-associate-theme/1090

features.css

/* Featured - original code
------------------------------------------------------------ */

.featured {
    margin: 0 auto;
    height: 430px;
    padding: 0 0 25px;
    width: 910px;
}

/* Add this next part in */
.featured-left {
    float:left;
    width:670px;
}

.featured-right {
    float:right;
    width: 220px;
}