For the rounded corner part, it's certainly possible in that there's nothing in the script that will hinder you from customizing the look of the drop down menus, which are simply DIVs on the page:
Code:
<!--1st drop down menu -->
<div id="dropmenu1_b" class="dropmenudiv_b">
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C1/">Horizontal CSS Menus</a>
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C2/">Vertical CSS Menus</a>
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C4/">Image CSS</a>
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C6/">Form CSS</a>
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C5/">DIVs and containers</a>
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C7/">Links and Buttons</a>
<a href="http://www.dynamicdrive.com/style/csslibrary/category/C8/">Other</a>
</div>
How you go about doing this though is beyond the scope of this script. You may want to do a search on Google for rounded corner divs, and go from there.
Regarding adding a small icon graphic, if you mean within the menu links of the drop down menus (like above), that's possible as well.
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