I think this can actually be done rather easily without messing with floats, or positioning. Just using a bit of CSS ought to do the trick.
CSS Section:
#heading {
text-align:center;
}
#headimage {
background-image:url(images/someimage.jpg);
background-repeat:no-repeat
}
And the xhtml to go with it:
<div id="heading">
<div id="headimage">
<p>Title Here</p>
</div>
</div>
I tested this very hastily in firefox and IE 6 in Windows, and it appeared to work fine. Let me know if any of this is unclear, and I'll try to say it better.