there is a way to edit a the css file to show rounded tabs instead of square. I think it uses the following code
-moz-border-radius-topleft: 4px;
border-top-left-radius: 4px;
-moz-border-radius-topright: 4px;
border-top-right-radius: 4px;
this will only work for tabs on top.
if this doesn’t work, or it isn’t enouph info, just reply.