In you stylesheet.css

find:
#productAdditionalImages {
width: 700px;
float: left;
margin-left: -120px;
margin-bottom: 40px;
}

change to:
#productAdditionalImages {
width:100%;
margin-top:-170px;
}

you could also add this so the images don't look like they are on top of each other.

.additionalImages {
padding:10px;
}


hope this helps!