Cases y condicionales

[programeitor]

<script>
functioncomprueba(radio){// programeitor 2005 ,diferente accion segun radio boton
if(radio[0].checked){if(document.sol.la.value==""){alert('elcampoLAestavacio');return;}}
if(radio[1].checked){if(document.sol.si.value==""){alert('elcampoSIestavacio');return;}}
document.sol.submit()
}
</script>

<formname=sol>
<inputname="re"type="radio"value="fa">
LA <inputname="la"type="text">
<br>
<inputname="re"type="radio"value="mi">
SI <inputname="si"type="text">
<p>
<inputtype="button"value="comprobar"onclick=comprueba(document.sol.re)>
</form>

El boton de envio ponlo type="button".