on the Second tab "Gallery", inside the Tab2 Content there's a Div with ID = "gallery", it's width is set to 700px and also 10px padding on all sides. That makes that div 720px wide, where the container is only 660px wide with 20px on each side.
So you should set your <div id="gallery"> width to 640px if you want 10px padding.
Same thing applies to tabs 3 and 4 i think. There's some div's inside those tabs that are too wide for the container.
Hope that helps, by the way really nice website, all the best.