function MM_showHideLayers() { //v6.0
  var i,p,v,obj,args=MM_showHideLayers.arguments;
  for (i=0; i<(args.length-2); i+=3) if ((obj=MM_findObj(args[i]))!=null) { v=args[i+2];
    if (obj.style) { obj=obj.style; v=(v=='show')?'visible':(v=='hide')?'hidden':v; }
    obj.visibility=v; }
}



function checkLogin(tf) {

    if (formatoCorrectoLogin(tf)) tf.submit();

}


function formatoCorrectoLogin (tf) {
	if (tf.loginname.value == '') {
		alert("Faltan datos obligatorios");
		return false;
	}
	if (tf.loginPassword.value == '') {
		alert("Faltan datos obligatorios");
		return false;
	}
	
	return true;
}


<!--
function checkSearchform(errorMsg) {
	
		if (document.searchform.keywords.value == '') {
			alert (errorMsg);
			return false;
		} else {
			document.searchform.submit();
			return true;
		}
		
	
	}

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_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_findObj(n, d) { //v4.01
  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 && d.getElementById) x=d.getElementById(n); return x;
}

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_openBrWindow(theURL,winname,features) { //v2.0
  window.open(theURL,winname,features);
}
//-->
function isValidEmail(str) {
   return (str.indexOf(".") > 2) && (str.indexOf("@") > 0);
 
}

function check_email_envia(f) {
			
			if( !isValidEmail(f.email_orig.value) ) {
				alert("El teu correu és incorrecte");
				f.email_orig.focus();  
				f.email_orig.style.background = "yellow";
				return false
			}
			
			if( !isValidEmail(f.email_dst.value) ) {
				alert("El correu destí és incorrecte");
				f.email_dst.focus(); 
				
				f.email_dst.style.background = "yellow";
				
				return false
			}
		
		
		return true;
}
function check_email_question(f) {
			
			if( !isValidEmail(f.email.value) ) {
				alert("El teu correu és incorrecte");
				f.email.focus();  
				return false
			}
			
			if( !(f.name.value) ) {
				alert("Indica el teu nom");
				f.name.focus();  
				return false
			}
		
		
		return true;
}