Hi rmu
Try adding the following to the Custom CSS field of your templates parameters...
#hornav .mainMenuParentBtn {
background: url(../images/arrow_down.png) right 50% no-repeat !important;
padding-right:18px;
}
#hornav .mainMenuParentBtnFocused {
background: url(../images/arrow_down_over.png) right 50% no-repeat !important;
padding-right:18px;
}
CiarĂ¡n