those images are set in the themes css. for the pile of boxes:
/webassist/themes/Purple/css/purple_styles.css
#main .banner .info {
background: url("../images/example.featured.png") no-repeat scroll 600px 60px transparent;
height: 262px;
padding: 40px 0 0;
width: 933px;
}
and for the transparent background:
/webassist/themes/Purple/css/configurable.css
.ps_pod4 {
background-color: #5B3A78;
background-image: url("../images/bg.banner.png");
}