function showCountries(continentID)
{
	var country = document.getElementById("f_adv_country");
	var optgroups = country.getElementsByTagName("optgroup");
	if(continentID == "0")
	{
		for (var i=0; i<optgroups.length; i++) {
			optgroups[i].style.display = "block";
			
			// select the first option by default
			var options = country.getElementsByTagName("option");
			if (options[0].value == "0")
				options[0].selected = "1";
		}
	}
	else
	{
		for (var i=0; i<optgroups.length; i++) {
			if (optgroups[i].id == continentID)
			{
				optgroups[i].style.display = "block";
				
				// select the first option by default
				var options = country.getElementsByTagName("option");
				if (options[0].value == "0")
					options[0].selected = "1";
				else
				{
					// get first item in first optgroup
					var options = optgroups[i].getElementsByTagName("option");
					if (options.length > 0)
						options[0].selected = "1";
				}
				
			}
			else
				optgroups[i].style.display = "none";
		}
	}
}