function busca(valor){ 


var valor_campo = document.form1.b_termo.value;
var url = valor+valor_campo;
  
xmlRequest.open("GET",url,true);
xmlRequest.onreadystatechange = mudancaEstado;   
xmlRequest.send(null);   
  
if (xmlRequest.readyState == 1) {   
document.getElementById("conteudo_mostrar").innerHTML = "<img src='images/carregando.gif'>";   
}   

return url;   

function mudancaEstado(){   
if (xmlRequest.readyState == 4){   
document.getElementById("conteudo_mostrar").innerHTML = xmlRequest.responseText;   
}   
}


}