[Richard M]

If you want to center a <div> all you need to do is this CSS:

#centerlayer {
width: 75%; /* Example width */
margin-left: auto;
margin-right: auto;
}

I usually find that this is useful for browsers with good CSS support, I used it on the nthellworld.co.uk homepage:

body {
max-width: 1024px; /* IE doesn't support advanced CSS so this will not work in that browser */
margin-left: auto;
margin-right: auto;
}