The following CSS should hide the righthand menu strip on gallery pages :-

.outside_table { width: 100% !important; }<br></br>.outer_content_cell { width: 100% !important; }<br></br>.content_table { width: 100% !important; }<br></br>.outside_nav2_cell { min-width: 0 !important; max-width: 0 !important; overflow: hidden; }<br></br>.content_cell { background-image: none; width: 100% !important; }

I think that's the best that's possible at the moment.
Still a little untidy looking, but at least the image isn't partialy hidden, and the whole width of the browser window is used.