@rhino79: I think it is because ADE does not honor auto-margins, and sets them to zero.
The paragraph method that Toxaris suggested works to keep the image centered, but if you want a div --
Since you are setting a width anyway, try setting a specific margin, such as this:
Code:
div.centered {
width: 75%;
margin-left: 12.5%;
margin-right: 12.5%;
text-align: center;
text-indent: 0;
}
(I always add the zero indent to make sure nothing causes the contents to be indented and thus display off-center)