Help separating my sidebar from my posts!

There isn’t enough room to float a 400px wide post inside a content area that’s only 600px wide and already holds a 320px wide sidebar. That’s just basic arithmetic. You would need to reduce 400px to 220px in

#noticias {
    float: left;
    margin: 0;
    padding: 0 10px;
    text-align: justify;
    width: 200px;
}