Event.observe(window, 'load', addObservers);

function addObservers()
{
	$('county').observe('change', showMembersByCounty)
}

function showMembersByCounty()
{
	var value = $('county').value;
	var update = new Ajax.Updater('members', '/admin/members.php', {
		parameters:{ county: value }
	})
}