thanks for the replies guys.
Neilo - i did a whole site search for 748 pixels, (after seeing the width setting in firebug) and can't find it anywhere.
on slideshow dissolve, this does seem to fix the width problem when entering the value in firebug, but i don't know where the line is in the code
Justin - i dont really mind what width the slideshow adopts, as long as it sits in the middle of the content div and the width of the div remains the same as in my screen.css.
what i am doing here, is a simple page layout, with the gallery info stored in a table.
the navigation menu will open a single page, (with appropriate url parameter to filter my recordset) and show the appropriate embedded gallery
one further thing, on a totally separate topic, i set up a css menu, and when the gallery format on display is fullsize_ribbon_lightbox, it isn;t possible to choose a menu subitem if that item is over the fullsize image.
(if this isn't clear I will make a new post with a link)
cheers again for all your support, (i seem to be asking more questions than providing answers at the moment)