CSS の z-index 属性は、任意の要素を別の要素の前または後ろに配置するトリックを行う必要があります。そのようです:
<style type="text/css">
body, html {
margin:0 auto;
padding:0;
font-family:Verdana, Geneva, sans-serif;
font-size:12px;
}
/* Header Styling */
#header {
color:#FFF;
background: url(/images/header-back.png) repeat-x;
position:fixed;
top:0;
left:0;
width:100%;
height:50px;
z-index:1;
}
#headerWrap {
width:1024px;
margin:0 auto;
height:50px;
}
/* Sub Header */
#subHeader {
position:fixed;
top:50px;
margin:0 auto;
z-index:1;
}
#subHeaderWrap {
height:30px;
width:830px;
border-bottom:thin solid #333;
background: url(../images/subheader.png) repeat-x;
}
/* Contaier */
#container {
margin:0 auto;
width:1024px;
min-height:600px;
}
#containerWrap {
margin-top:50px;
}
/* Menu */
#sidebar {
float:left;
width:140px;
min-height:600px;
}
#content {
border-left:#333333 solid thin;
border-right:#333333 solid thin;
border-bottom:#333333 solid thin;
float:left;
width:830px;
min-height:600px;
padding-top:30px;
margin-bottom:10px;
}
#contentWrap {
width:830px;
margin:0 auto;
padding-bottom:10px;
}
</style>
<div id="container">
<div id="header" style="z-index:1;"/* Places div on top */">
This is transparent.
</div>
<div id="containerWrap">
<div id="sidebar">
Menu Items Here
</div>
<div id="content">
<div id="contentWrap">
<div id="subHeader" style="z-index:1;"/* Places div on top */">
<div id="subHeaderWrap">
This div is transparent too, but is now on top.
</div>
</div>
Anything here is scrollable and will scroll under the divs above with z-index:1;
</div>
</div>