The Pro version of WPSP has a lot more styling control – for the free version some CSS like this:
.wp-show-posts-inner {
border: 1px solid #000;
padding-bottom: 20px;
}
.wp-show-posts-entry-header, .wp-show-posts-entry-summary, .wp-show-posts-entry-meta {
padding-left: 20px;
padding-right: 20px;
}