Changing column with on CSS Fixed Layout #2.1

[joketribe.com]

1) Script Title: CSS Fixed Layout #2.1- (Fixed-Fixed)

2) Script URL (on DD): http://www.dynamicdrive.com/style/layouts/item/css-fixed-layout-21-fixed-fixed/

3) Describe problem: Trying to change column widths, but not having complete success. It seems to be related to the use of an image in the header, but I'm interested in finding out why that is the case, as the image is 728px wide and the maincontainer is also 728px wide (the newly defined width.)

The url to the test page is http://www.joketribe.com/test1219.php

Can anyone provide any suggestions?

Thanks!

[joketribe.com]

Looks like I was on the right path. The 728px wide header image was too wide. resizing it to be narrower (I had to go down to 708px wide or narrower) made things OK. Can anyone tell me if this is due to padding, or to margins? And if so, which attribute on which container?

Thanks.