var letters=' ABCÇDEFGHIJKLMNÑOPQRSTUVWXYZabcçdefghijklmnñopqrstuvwxyzàáÀÁéèÈÉíìÍÌïÏóòÓÒúùÚÙüÜ'
var numbers='1234567890'
var signs=',.:;@-\''
var mathsigns='+-=()*/'
var custom='<>#$%&?¿'
/* uso
<input type="text" onkeypress="return alpha(event,numbers)" />
  <input type="text" onkeypress="return alpha(event,letters)" />
  <input type="text" onkeypress="return alpha(event,numbers+letters+signs)" />

  */
function alpha(e,allow) {
     var k;
     if(e.which<=15)
     	return true;
     k=document.all?parseInt(e.keyCode): parseInt(e.which);
     return (allow.indexOf(String.fromCharCode(k))!=-1);
}