"change the float to center"
You can only float left or right; specifying "center" would cause a css error.
To center the contents of an element, use
text-align: center;
Your stylesheet_main.css has this:
#productAdditionalImages {margin:10px; border:1px solid #535353; padding:10px 0px;}
#productAdditionalImages .additionalImages {text-align:center;}
#productAdditionalImages .additionalImages a {color:#C00505; font-weight:bold;}
I didn't see any conflicts in your other two major stylesheets, or the mod stylesheets, but that's not to say there aren't any. The more separate files you have (unless they are tightly focused like styles_AJAX_image_swapper.css), the easier it is to miss conflicts.
Your template maker has changed some of the standard ids and classes, so some standard suggestions may not apply to you, or there may be unknown styling that overrides the standard suggestions. At least they have not eliminated or encrypted most of the standard identifiers, as many Template Monster templates do.



