Dirty Fix working
Ok, this may not be the best solution, but it seems to work ok.
as the js was resizing the outerwrapper div, what i did was rename the outerwrapper div in my screen.css to outerwrapperfixed.
i created a new outerwrapper div with left and right margins of auto, and placed it in within my content div, thinking that whatever the width of the js outerwrapper div, it would always be centred in the content div.
it may not be semanitically correct as the js outerwrapper isn't the outerwrapper, but i don't know what the implications are of renaming the div in the js file, so i left it asis.
i have updated the files on the server.
i also added a (not yet working) css menu across the full width of the div, (which is why the constant width was important).
this causes a separate problem with the menu over a lightbox gallery which i'll raise in a different post.
now all i want to do to this layout is make the footer stick to the bottom!
(more hair loss)