Well, in order position the text correctly, the div that all of your content is wrapped around needs to be set to position:relative in the css, it is usually called #wrapper.
If you add the following code just under your wrapper div, likely to look like this: <div id=”wrapper”> in your header.php file:
<div class=”top_text”>
This is your text…
</div>
And then add the following code to your stylesheet/css:
.top_text{
position:absolute;
top:0;
left:0;
background:#0099CC;
color:#FFF
padding:10px;
}
That will put a blue box at the top left of your site, but you can play around with the css to get it to look how you want.
Hope this helps