function ventana(imagename, ancho, alto){
ancho=ancho+20
alto=alto+30
if (ancho > 760) {ancho=760;};
if (alto > 650) {alto=650;};
window.open(imagename,"Imagen","menubar=no,scrollbars=yes,status=no,width="+ancho+",height="+alto+", top=0, left=0, screenX=0, screenY=0")
}


  
 


<!--
function MM_validateForm() { //v4.0
  var i,p,q,nm,test,num,min,max,errors='',args=MM_validateForm.arguments;
  for (i=0; i<(args.length-2); i+=3) { test=args[i+2]; val=MM_findObj(args[i]);
    if (val) { nm=val.name; if ((val=val.value)!="") {
      if (test.indexOf('isEmail')!=-1) { p=val.indexOf('@');
        if (p<1 || p==(val.length-1)) errors+='- '+nm+', introduzca una direccion de correo.\n';
      } else if (test!='R') { num = parseFloat(val);
        if (isNaN(val)) errors+='- '+nm+', introduzca un número.\n';
        if (test.indexOf('inRange') != -1) { p=test.indexOf(':');
          min=test.substring(8,p); max=test.substring(p+1);
          if (num<min || max<num) errors+='- '+nm+' must contain a number between '+min+' and '+max+'.\n';
    } } } else if (test.charAt(0) == 'R') errors += '- '+nm+'.\n'; }
  } if (errors) alert('Para atenderle correctamente debe rellenar:\n'+errors);
  document.MM_returnValue = (errors == '');
}
//-->



<!-- Begin
function lista(form1){
var URL = document.form1.site.options[document.form1.site.selectedIndex].value;
window.location.href = URL;
}
// End -->