... ma almeno funzia!

// JavaScript Document

var curdate = new Date();
var curday = ((curdate.getDate()) +2 ); // day
var curmonth = curdate.getMonth(); // 0 is January, December is 11

function checkday(fm_search) {
var attuale=new Date();
//alert ("Data di oggi :" + attuale);
//var g=parseInt(fm_search.Dep_Day[fm_search.Dep_Day.selectedIndex].value);
var g=(fm_search.Dep_Day[fm_search.Dep_Day.selectedIndex].value);
var m=((fm_search.Dep_Month[fm_search.Dep_Month.selectedIndex].value)-1);
var a=(fm_search.Dep_Year[fm_search.Dep_Year.selectedIndex].value);
var datapartenza=new Date(a, m, g);
//alert ("data di partenza :" + datapartenza);
var giornidifferenza=Math.ceil((datapartenza-attuale)/1000/60/60/24); // calcolo i giorni che intercorrono tra oggi e la data scelta
if (giornidifferenza < 3) {
alert("You cannot book a ticket on this day. \n You have to book with at least 3 days of advance.");
// reset the date to a correct one
document.fm_search.Dep_Day.options.selectedIndex = curday;
document.fm_search.Dep_Month.options.selectedIndex = curmonth;
return false;
}
else {
// if everything is okay change the return date.
document.fm_search.Rtn_Day.options.selectedIndex = g;
document.fm_search.Rtn_Month.options.selectedIndex = m;
}
}

adesso devo raffinarlo un po!

grazie 1000