// Allows only one checkbox to be selected at one time
// add onclick="SingleSelect('product_type',this);" to your checkbox

function SingleSelect(regex,current)
	{
	re = new RegExp(regex);
	
	for(i = 0; i < document.forms[0].elements.length; i++)
		{
		elm = document.forms[0].elements[i];
		
		if (elm.type == 'checkbox')
			{
			if (re.test(elm.name))
				{
				elm.checked = false;
				}
			}
		}
	current.checked = true;
	}