Some of the boxes are set to left justifed ("Please Note" black and red one and the bricks/sherman pair) and the rest is centred. This means the centred ones will "move" right as people view with larger screen resolutions.
On my web sites, I use frames and make the centre one a fixed 1024 pixels wide. The ones either side have no content and just change size to suit the screen resolution. This means that the site will look the same to anyone with their screen set to 1024 or wider.
See
http://www.shermanm4a3.co.uk for the layout - please excuse the content - it's a work in progress and somewhat low on my list of things to do !!
Adrian.