[Trevor Matthews]

The real solution was to make the image the correct size, in my case 1300px wide and 90px high.

I uploaded it and then found the vbulletin-chrome.css template

I added the following to the code overflow: hidden;

As shown below.

.doc_header {
_background-image:none;
border:{vb:stylevar header_border};
color:{vb:stylevar header_color};
font:{vb:stylevar header_font};
position:relative;
min-height:35px;
overflow: hidden;

doc_width was then set to 1300px
doc_margin was set to left and right auto
doc_minwidth was set to 1000px
doc_width was set to 90%

My logo image is now correctly aligned on all screen types and sizes.