*dies*
I'm so sorry leylandfor, but you have definitely made my laugh of the month.
Adjusting the width in photoshop did nothing but keep he image at the same size (100%), the percentage of the image is much different than the width percentage (in width) of your header's html.
It's like if i tell you I want a shirt that stretches fully accross my arms and you tell a tailor to make the dimensions of my shirt 100% of what it currently is (which in reality keeps it the same) as oppose to adjusting the sewing/cut accordingly (not much of a tailor, but hope you can catch the metaphor).
I think what you're looking to do is the following.
In your header template search for
<table border="0" width="100%" cellpadding="0" cellspacing="0" align="center">
Replace it with:
<table border="0" width="100%" cellpadding="0" cellspacing="0" align="center" bgcolor="#ffffff">
This will make your header's table background white, which will probably create the effect you'd like.