Your #container should be outside of the #header-wrap, then specify a fixed height for #header-wrap, after, specify margin-top for #container equal to the #header-wrap’s height. Something like this:
#header-wrap {
position: fixed;
height: 200px;
top: 0;
width: 100%;
z-index: 100;
}
#container{
margin-top: 200px;
}
Hope this is what you need:
http://jsfiddle.net/KTgrS/