When you use this code you can choose the exact position of the thing you want.

<div id="nav" style="position:absolute; left:200px; top:200px; width:200px;"> Content goes here </div>

Where it says left just change it to the number you want your thing on your page to go left.
Where it says top just change it to the number you want your thing on your page to go to the top.
Where it says width just change it to the number to the width you want on your thing.