var isNN = (navigator.appName.indexOf("Netscape")!=-1);

function AtivaEnter(evento, NomeBotao)
{
    var botao = document.getElementById(NomeBotao);
    var keyCode = (isNN) ? evento.which : evento.keyCode;

    if ( keyCode == 13 )
    {
        evento.preventDefault? evento.preventDefault() : evento.returnValue = false;
        alert(botao);
        botao.click();
    }
}