CSS
div#container {
width:400px;
height: 400px;
padding:50px;
background: red;
}
div.leftbox {
float: left;
width:175px;
height: 175px;
margin-bottom: 50px;
background: blue;
}
div.rightbox {
float: right;
width: 175px;
height: 400px;
background: yellow;
}
HTML
<div id="container">
<div class="rightbox">
Right Image Box
</div>
<div class="leftbox">
Left Image Box Top
</div>
<div class="leftbox">
Left Image Box Bottom
</div>
</div>