I do this at my site by making the header a background image in a cell.
Here is a sample of the css:
<br />.logo { <br />background-image: url(http://www.yoursite.com/image.gif); <br />padding: 0px; <br />height: 90px; <br />width: 500px; <br />background-repeat: no-repeat; <br />} <br />
Then you just have to edit your header by adding the logo class to the appropriate td tag.