Código (html4strict) [Seleccionar]
<head>
<script type="text/javascript">
function submit(flota) {
evento = window.event;
if(evento.keycode==13) {
flota.submit();
}
}
</script>
<form id="form1" method="post" action="busqueda.php" onkeypress="submit(this.form);">
<input name="palabra" type="text" id="palabra" />
<input name="buscador" type="submit" id="buscador" value="Buscar" />
</form>
eso te sirve4??