its pretty simple. you just have to use Position:Relative in the Container div and wrap a <center> tag around it. check this example
CSS Style Sheet:
<style type="text/css">
.container{
position:relative;
width:800px;
background:#CCCCCC;
height:400px;
text-align:left;
}
.div1{
position:absolute;
width: 260px;
height: 177px;
left: 121px;
top: 122px;
background-color:#666666
}
</style>
HTML Code:
<center>
<div class="container">
<div class="div1">
</div>
</div>
</center>
