var filter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;

function validate_join(form)
{
	if (form.email.value.length<1){
        alert("Please enter an email address.");
        form.email.focus();
        return false;
    }
    if (!filter.test(form.email.value)){
        alert("Please enter a valid email address.");
        form.email.select();
        form.email.focus();
        return false;
    }
}