function fechaPopUp(xCampo){
		var Campo = document.getElementById(xCampo);
		var arrFecha;
		if(Campo.value.length!=0){
			arrFecha = Campo.value.split('/');
			openCal(arrFecha[2],arrFecha[1],arrFecha[0],'frmCriterio.'+xCampo);
		}else{
			openCal(0,0,0,'frmCriterio.'+xCampo);
		}
	}
			
function hoy () {
	var today = new Date() ;
	return (((today.getDate()  <= 9) ? "0" : "") + today.getDate() + "/" + (today.getMonth()+1)+ "/" + today.getFullYear());
}

function maniana () { 
	var tomorrow = new Date() ;
	var tomorrow = new Date(tomorrow.getTime() + 1*24*60*60*1000) ;
	return ( ((tomorrow.getDate()  <= 9) ? "0" : "") + tomorrow.getDate() + "/" + (tomorrow.getMonth()+1)+ "/" + tomorrow.getFullYear());

}


function siguientes7Dias () { 
	var tomorrow = new Date() ;
	var tomorrow = new Date(tomorrow.getTime() + 7*24*60*60*1000) ;
	if (tomorrow.getDate()  <= 9) {
		var Fecha7 = "0" + tomorrow.getDate() + "/" + (tomorrow.getMonth()+1)+ "/" + tomorrow.getFullYear() ;
	} else { 
		var Fecha7 = tomorrow.getDate() + "/" + (tomorrow.getMonth()+1)+ "/" + tomorrow.getFullYear() ;
	};
	return (Fecha7);
}

function MesFechaDia1 () { 
	var tomorrow = new Date() ;
	var tomorrow = new Date(tomorrow.getTime() + 7*24*60*60*1000) ;
	var Fecha = "01" + "/" + (tomorrow.getMonth()+1)+ "/" + tomorrow.getFullYear() ;
	return (Fecha);
}

function MesFechaDia30 () { 
	var tomorrow = new Date() ;
	var tomorrow = new Date(tomorrow.getTime() + 7*24*60*60*1000) ;
	var Fecha = "30" + "/" + (tomorrow.getMonth()+1)+ "/" + tomorrow.getFullYear() ;
	return (Fecha);
}

<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->
<!-- Original:  Torsten Frey (tf@tfrey.de) -->
<!-- Web Site:  http://www.tfrey.de -->

<!-- Begin
function check_date(field){
var checkstr = "0123456789";
var DateField = field;
var Datevalue = "";
var DateTemp = "";
var seperator = "/";
var day;
var month;
var year;
var leap = 0;
var err = 0;
var i;
   err = 0;
   DateValue = DateField.value;
   /* Delete all chars except 0..9 */
   for (i = 0; i < DateValue.length; i++) {
	  if (checkstr.indexOf(DateValue.substr(i,1)) >= 0) {
	     DateTemp = DateTemp + DateValue.substr(i,1);
	  }
   }
   DateValue = DateTemp;
   /* Always change date to 8 digits - string*/
   /* if year is entered as 2-digit / always assume 20xx */
   if (DateValue.length == 6) {
      DateValue = DateValue.substr(0,4) + '20' + DateValue.substr(4,2); }
   if (DateValue.length != 8) {
      err = 19;}
   /* year is wrong if year = 0000 */
   year = DateValue.substr(4,4);
   if (year == 0) {
      err = 20;
   }
   /* Validation of month*/
   month = DateValue.substr(2,2);
   if ((month < 1) || (month > 12)) {
      err = 21;
   }
   /* Validation of day*/
   day = DateValue.substr(0,2);
   if (day < 1) {
     err = 22;
   }
   /* Validation leap-year / february / day */
   if ((year % 4 == 0) || (year % 100 == 0) || (year % 400 == 0)) {
      leap = 1;
   }
   if ((month == 2) && (leap == 1) && (day > 29)) {
      err = 23;
   }
   if ((month == 2) && (leap != 1) && (day > 28)) {
      err = 24;
   }
   /* Validation of other months */
   if ((day > 31) && ((month == "01") || (month == "03") || (month == "05") || (month == "07") || (month == "08") || (month == "10") || (month == "12"))) {
      err = 25;
   }
   if ((day > 30) && ((month == "04") || (month == "06") || (month == "09") || (month == "11"))) {
      err = 26;
   }
   /* if 00 ist entered, no error, deleting the entry */
   if ((day == 0) && (month == 0) && (year == 00)) {
      err = 0; day = ""; month = ""; year = ""; seperator = "";
   }
   /* if no error, write the completed date to Input-Field (e.g. 13.12.2001) */
   if (err == 0) {
      DateField.value = day + seperator + month + seperator + year;
   }
   /* Error-message if err != 0 */
   else {
      //alert("Formato de fecha incorrecto en " + DateField.name + "!!");
      //DateField.select();
	  //DateField.focus();
	  return (false);
   }
   return (true) ;

}
//  End -->
//   	<INPUT type="text" name=testdat size='10' maxlength="10" onblur="check_date(this)">