[kh99]

I'm not really an html/css person, but I think this might work - edit your header template and put this at the very top:

<style type="text/css">
body {background-image:url('background.jpg');}
</style>
<div style="min-height:150px;"></div>

Of course you want to change background.jpg and 150 to the values you need.

I don't know abut transparency, maybe someone else will help.