My suggestion, You can combine AnyLink Drop Down Menu (http://www.dynamicdrive.com/dynamicindex1/dropmenuindex.htm) and DOM Image Rollover (http://www.dynamicdrive.com/dynamicindex15/domroll.htm)
Change this
<a href="default.htm" onClick="return clickreturnvalue()" onMouseover="dropdownmenu(this, event, menu1, '150px')" onMouseout="delayhidemenu()">Web Design</a>
to
<a href="default.htm" onClick="return clickreturnvalue()" onMouseover="dropdownmenu(this, event, menu1, '150px')" onMouseout="delayhidemenu()"><img src="before.gif" hsrc="after.gif"></a>
Hope that helps :)