If you are having multiselect picklist, value in multiselect can be set as
<script type="text/javascript">
function setValue()
{
var desiredValue = '{!JSENCODE(venueValue)}';
var selectedItem= window.parent.opener.document.getElementById(venueId+ '_selected');
var unselectedItem = window.parent.opener.document.getElementById(venueId + '_unselected');
for(var i=0; i<unselectedItem.options.length; i++) {
if ( unselectedItem.options[i].text == desiredValue ) {
selectedItem.appendChild(unselectedItem.options[i]);
unselectedItem.removeChild(unselectedItem.options[i]);
}
}
}
Here one should not forget to append _selected and _unselected to get Id for multiselect picklist.
If you are having single select picklist you just have to assign value and call onchange fuction so that dependent picklist value gets populated. It can be done as
<script type="text/javascript">
function setValue()
{
window.parent.opener.document.getElementById(venueId).value='{!JSENCODE(venueValue)}';
window.parent.opener.document.getElementById(venueId).onchange();
}
</script>