function apenasnumero(event){
var keyCode = event.keyCode ? event.keyCode : event.which ? event.which : event.charCode;
var caract = new RegExp(/[0-9]+$/i);
var caract = caract.test(String.fromCharCode(keyCode));

if(!caract){
alert("Caracter inválido: " +String.fromCharCode(keyCode));
keyCode=0;
return false;
}
}