You can use this Javascript to check if any option of a
select has been selected:
if (document.formname.fieldname.selectedIndex < 0) {
alert("Fieldname is required.");
return false;}
return true;
where formname is the name of the form, and fieldname is the
name of the select. The alert pops up the error message, and the
"return false;" prevents the form from being submitted. Put this
code in a Javascript function that you call from onsubmit in the
form tag, like so:
onsubmit="return functionname();"