Il tuo codice è molto confuso,
comunque parti da questo:
Codice PHP:
<td colspan="4"><div align="center">[url="?classeconfronto=a"]A[/url] - B - C - D - E - F - G - H - I - L - M - N - O - P - Q - R - S - T - V - Z</div></td>
</tr>
<?php
include ('config.php');
$query = "SELECT * FROM clienti";
$rispro = mysql_query($query);
while($immob = mysql_fetch_array($rispro)){
echo"
<tr>
<td width=\"53%\" bgcolor=\"#6699FF\"><span class=\"style6\">NomeAzienda</span></td>
<td colspan=\"3\" bgcolor=\"#6699FF\"><span class=\"style6\">Referente</span></td>
</tr>
";
$immobs = substr($immob,0,1)
switch($immobs){
case "A":
$classe=a;
break;
case "B":
$classe=b;
break;
case "C":
$classe=c;
break;
case "D":
$classe=d;
break;
case "E":
$classe=e;
break;
case "F":
$classe=f;
break;
case "G":
$classe=g;
break;
case "H":
$classe=h;
break;
case "I":
$classe=i;
break;
case "L":
$classe=l;
break;
case "M":
$classe=m;
break;
case "N":
$classe=n;
break;
case "O":
$classe=o;
break;
case "P":
$classe=p;
break;
case "Q":
$classe=q;
break;
case "R":
$classe=r;
break;
case "S":
$classe=s;
break;
case "T":
$classe=t;
break;
case "V":
$classe=v;
break;
case "Z":
$classe=z;
break;
}
if($classeconfronto==$classe){
echo"
<tr>
<td><a href=\"visualizza.php?cd=$immob[cd]\" class=\"style2\"><font size=\"3\" >
$immob[azienda]
</font></a>
</td>
<td colspan=\"3\" align=\"center\">
$immob[nome]
</font></span>
</td>
";
}
?>
</tr>
<? } ?>
</table>