Rendere visibile cella adiacente a quella attiva

[Xinod]

x es.

function cambia(e, obj){
	if(!e) e=window.event;
	var on=(e.type=='focus')?1:0;

	var vis=(on)?'visible':'hidden';
	var col=(on)?'brown':'transparent';

	obj.parentNode.style.backgroundColor=col;
	var onm=obj.name;
	var tdId='td_'+((onm=='indirizzo'||onm=='telefono'||onm=='email')?'altri':onm);
	document.getElementById(tdId).style.visibility=vis;
}

pero' conviene aggiungere identificativi, dal momento che gia' avrai name per i campi

<form>
<table>
<tbody>
<td>nome:</td>
<td><input type="text" name="nome" onfocus="cambia(event, this)" onblur="cambia(event, this)" /></td>
<td id="td_nome" style="visibility:hidden">inserisci il nome</td>
</tr>
<tr>
<td>cognome:</td>
<td><input type="text" name="cognome" onfocus="cambia(event, this)" onblur="cambia(event, this)" /></td>
<td id="td_cognome" style="visibility:hidden">inserisci il cognome</td>
</tr>
<tr>
<td>indirizzo:</td>
<td><input type="text" name="indirizzo" onfocus="cambia(event, this)" onblur="cambia(event, this)" /></td>
<td rowspan="3" id="td_altri" style="visibility:hidden">inserisci gli altri dati</td>
</tr><tr>
<td>telefono:</td>
<td><input type="text" name="telefono" onfocus="cambia(event, this)" onblur="cambia(event, this)" /></td>
</tr>
<tr>
<td>email:</td>
<td><input type="text" name="email" onfocus="cambia(event, this)" onblur="cambia(event, this)" /></td>
</tr>
</tbody>
</table>
</form>

ciao