function checkSelection()
{

	var checkbox_choices = 0;

	for (counter = 0; counter < document.checkbox_form.checkbox.length; counter++)
	{
		if (document.checkbox_form.checkbox[counter].checked)
		{ 
			checkbox_choices = checkbox_choices + 1; 
		}
	}
	
	if (checkbox_choices == 0 )
	{
		alert("U moet minmaal 1 week aanvinken om te kunnen reserveren")
		return (false);
	}
	return (true);
}