$(function (){
    $('input[name=email]').focus(function (){ var obj = $(this); if(obj.attr('value')=='Please enter a valid email.')obj.attr('value','').css({'color':'black'}) })

    $('form[name=signup]').submit(function (){
        var email = $('input[name=email]').val();
        var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
        if(reg.test(email)){
            $(self).submit();   
        }else{
            $('input[name=email]').attr('value','Please enter a valid email.').css({'color':'red'})
            return false;
        }
    })
})