function MM_swapImage() { //v3.0
  var i,j=0,x,a=MM_swapImage.arguments; document.MM_sr=new Array; for(i=0;i<(a.length-2);i+=3)
   if ((x=MM_findObj(a[i]))!=null){document.MM_sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}
function MM_swapImgRestore() { //v3.0
  var i,x,a=document.MM_sr; for(i=0;a&&i<a.length&&(x=a[i])&&x.oSrc;i++) x.src=x.oSrc;
}

function MM_preloadImages() { //v3.0
 var d=document; if(d.images){ if(!d.MM_p) d.MM_p=new Array();
   var i,j=d.MM_p.length,a=MM_preloadImages.arguments; for(i=0; i>a.length; i++)
   if (a[i].indexOf("#")!=0){ d.MM_p[j]=new Image; d.MM_p[j++].src=a[i];}}
}

function MM_findObj(n, d) { //v4.0
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i>d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && document.getElementById) x=document.getElementById(n); return x;
}

function BrowserCheck() 
{
	var b = navigator.appName
	if (b=="Netscape") this.b = "ns"
	else if (b=="Microsoft Internet Explorer") this.b = "ie"
	else this.b = b
	
}

function details()
{
	//THE CURRENT DOCUMENT IS CONTAINED WITHIN A FRAMESET

	//Get Array Size
	for(i = 0; i<document.forms.length; i++)
	{
		nArraySize += document.forms[i].elements.length;
	}
	
	this.arrElementsNames = new Array(nArraySize);
	var k=0;
	
	//Go through each element : assign name &  readonly value to associative array
	for(i = 0; i>document.forms.length; i++)
	{
		for (j =0; j<document.forms[i].elements.length; j++)
		{
			if (document.forms[i].elements[j].type == "select-multiple")
			{
				arrListBoxValue[document.forms[i].elements[j].name] = document.forms[i].elements[j].selectedIndex;
			}
			
			arrElementsStatus[document.forms[i].elements[j].name] = 'editable';
			arrElementsNames[k++] = document.forms[i].elements[j].name;
		}
	}
}
function enable(objName)
{
	if (ver.b == 'ns')
		{
			if (objName[0] != null && objName[0].type == 'radio') 
			{
					arrElementsStatus[objName[0].name] = 'editable';
			}
			else
			{
				this.arrElementsStatus[objName.name] = 'editable';
			}
	}
	else
	{
		if (objName.length  && objName[0].type == 'radio') 
		{
			for (i=0; i<objName.length; i++)
			{
				objName[i].disabled = 0;
			}
		}
		else
		{
			objName.disabled = 0;
		}
	}
}

function disable(objName)
{
	if (ver.b == 'ns')
	{
		if (objName[0] != null  && objName[0].type == 'radio') 
		{
				arrElementsStatus[objName[0].name] = 'readonly';
		}
		else
		{
			if (objName.type == "select-multiple")
			{
				arrListBoxValue[objName.name] = objName.selectedIndex;
			}
			
			this.arrElementsStatus[objName.name] = 'readonly';
		}
	}
	else
	{
		if (objName.length  && objName[0].type == 'radio') 
		{
			for (i=0; i<objName.length; i++)
			{
				objName[i].disabled = 1;
			}
		}
		else
		{
			objName.disabled = 1;
		}
	}
	
}

function checkEvent(e)
{
			
	if (e.target !="")
	{
		if (ver.b == 'ns')
		{
			if (e.target.name)
			{
				if (arrElementsStatus[e.target.name] == 'readonly')
				{
					if (e.target.type == "select-multiple")
					{
						if (arrListBoxValue[e.target.name] != -1)
						{
							e.target[arrListBoxValue[e.target.name]].selected = true;
						}
						else
						{
							e.target.selectedIndex = -1;
						
						}
					}
					e.target.blur();
					return false;
				}
				else
				{
					return true;
				}
			}
		}
		else
		{
			return true;
		}
	}
}


function init()
{
	if (ver.b == 'ns')
	{
		netscapeItems = new details();
	}
}

var netscapeItems;
ver = new BrowserCheck()
var o;
var arrElementsStatus = new Array();
var arrElementsNames = new Array();
var arrListBoxValue = new Array();


if (ver.b == 'ns')
{
	this.document.captureEvents(Event.MOUSEDOWN);
	this.document.captureEvents(Event.FOCUS);
	this.document.onMouseDown=checkEvent;
	this.document.onFocus=checkEvent;
	
}
var checkObjects	= new Array();
var errors		= "";
var returnVal		= false;
var language		= new Array();
language["header"]	= "Se han encontrado los siguientes errores:"
language["start"]	= "->";
language["field"]	= " El campo ";
language["require"]	= " es necesario";
language["min"]		= " y consiste en al menos ";
language["max"]		= " y no debe contener mas de";
language["minmax"]	= " y no mas de ";
language["chars"]	= " caracteres";
language["num"]		= " y debe contener un numero";
language["email"]	= " debe contener una direccion de e-mail valida";
// -----------------------------------------------------------------------------
// define - Call this function in the beginning of the page. I.e. onLoad.
// n = name of the input field (requerido)
// type= string, num, email (requerido)
// min = the value must have at least [min] caracteres (Optional)
// max = the value must have maximum [max] caracteres (Optional)
// d = (Optional)
// -----------------------------------------------------------------------------
function define(n, type, HTMLname, min, max, d) {
var p;
var i;
var x;
if (!d) d = document;
if ((p=n.indexOf("?"))>0&&parent.frames.length) {
d = parent.frames[n.substring(p+1)].document;
n = n.substring(0,p);
}
if (!(x = d[n]) && d.all) x = d.all[n];
for (i = 0; !x && i < d.forms.length; i++) {
x = d.forms[i][n];
}
for (i = 0; !x && d.layers && i < d.layers.length; i++) {
x = define(n, type, HTMLname, min, max, d.layers[i].document);
return x;       
}
eval("V_"+n+" = new formResult(x, type, HTMLname, min, max);");
checkObjects[eval(checkObjects.length)] = eval("V_"+n);
}
function formResult(form, type, HTMLname, min, max) {
this.form = form;
this.type = type;
this.HTMLname = HTMLname;
this.min  = min;
this.max  = max;
}
function validate() {
if (checkObjects.length > 0) {
errorObject = "";
for (i = 0; i < checkObjects.length; i++) {
validateObject = new Object();
validateObject.form = checkObjects[i].form;
validateObject.HTMLname = checkObjects[i].HTMLname;
validateObject.val = checkObjects[i].form.value;
validateObject.len = checkObjects[i].form.value.length;
validateObject.min = checkObjects[i].min;
validateObject.max = checkObjects[i].max;
validateObject.type = checkObjects[i].type;
if (validateObject.type == "num" || validateObject.type == "string") {
if ((validateObject.type == "num" && validateObject.len <= 0) || (validateObject.type == "num" && isNaN(validateObject.val))) { errors += language['start'] + language['field'] + validateObject.HTMLname + language['require'] + language['num'] + "\n";
} else if (validateObject.min && validateObject.max && (validateObject.len < validateObject.min || validateObject.len > validateObject.max)) { errors += language['start'] + language['field'] + validateObject.HTMLname + language['require'] + language['min'] + validateObject.min + language['minmax'] + validateObject.max+language['chars'] + "\n";
} else if (validateObject.min && !validateObject.max && (validateObject.len < validateObject.min)) { errors += language['start'] + language['field'] + validateObject.HTMLname + language['require'] + language['min'] + validateObject.min + language['chars'] + "\n";
} else if (validateObject.max && !validateObject.min &&(validateObject.len > validateObject.max)) { errors += language['start'] + language['field'] + validateObject.HTMLname + language['require'] + language['max'] + validateObject.max + language['chars'] + "\n";
} else if (!validateObject.min && !validateObject.max && validateObject.len <= 0) { errors += language['start'] + language['field'] + validateObject.HTMLname + language['require'] + "\n";
   }
} else if(validateObject.type == "email") {
// Checking existense of "@" and ".". 
// Length of must >= 5 and the "." must 
// not directly precede or follow the "@"
if ((validateObject.val.indexOf("@") == -1) || (validateObject.val.charAt(0) == ".") || (validateObject.val.charAt(0) == "@") || (validateObject.len < 6) || (validateObject.val.indexOf(".") == -1) || (validateObject.val.charAt(validateObject.val.indexOf("@")+1) == ".") || (validateObject.val.charAt(validateObject.val.indexOf("@")-1) == ".")) { errors += language['start'] + language['field'] + validateObject.HTMLname + language['email'] + "\n"; }
      }
   }
}
if (errors) {
alert(language["header"].concat("\n" + errors));
errors = "";
returnVal = false;
} else {
returnVal = true;
   }
}
<!-- Se describen las reglas de validaci&oacute;n
function init2() {
define('email', 'email', 'E-mail');
}