Here, this ones working. :)
upd: Just in case jsfiddle is not responding here is the code...
CSS:
.holder{
width:100%;
display:block;
}
.content{
background:#fff;
padding: 28px 26px 33px 25px;
}
.popup{
border-radius: 7px;
background:#6b6a63;
margin:30px auto 0;
padding:6px;
// here it comes
position:absolute;
width:800px;
top: 50%;
left: 50%;
margin-left: -400px; // 1/2 width
margin-top: -40px; // 1/2 height
}
HTML:
<div class="holder">
<div id="popup" class="popup">
<div class="content">some lengthy text</div>
</div>
</div>