If you want images centred (when smaller than your width) you could try adding the below to the <div> that holds the slideshow:
Actually I've just had another look at your site.
It might look better with padding bottom and top removed, try replacing all the #FlashHeadpiece with this:
#FlashHeadpiece {
text-align:center;
background-color:#222222;
border-bottom-width: 1px;
border-top-style: solid;
border-right-style: solid;
border-bottom-style: solid;
border-left-style: solid;
border-top-color: #CCCCCC;
border-right-color: #CCCCCC;
border-bottom-color: #333333;
border-left-color: #CCCCCC;
border-top-width: 0px;
border-right-width: 0px;
border-left-width: 0px;
}
Additionally you are getting some styling from the slideshow component you are using - the css for this is located here on your site:
modules/mod_jw_sir/mod_jw_sir/mod_jw_sir.css
You might have some luck with image centering if you open the above css style sheet and ad a rule for ul#jw-sir
If there is already a rule ad text-align:center; to it, otherwise create one:
ul#jw-sir {
text-align:center;
}
Let me know if that works