header is separated from body – Can’t figure it out

In the style definitions for the JoomlaWorks “Frontpage Slideshow”, you will need to change the margins:

#fpss-outer-container {margin:8px auto 0;padding:2px;border:1px solid #999;overflow:hidden;width:910px;height:308px;}

and in your themes style sheet change the header padding :

#header
{
margin: 0;
padding-bottom: 1px;
}

Those two changes seem to do it in firebug. Make a backup first if you decide to try it, and test it in more than one browser of course.