PHP - RE:Manejo de Chekbox en php

<?php
$valor = $_POST ['COMBO_SECCION'];
$link = mysql_connect("localhost", "root", "");
mysql_select_db("ayudasalud",$link);
$sql = "select * from centro_atencion, medico
where medico.rut_med = centro_atencion.rut_med && centro_atencion.nomb_centro=$valor";
$do = mysql_query($sql) or die ("Error en query < br >".mysql_error());
print ("<TABLE BORDER =1 WITDH=\"\75%\" CELLSPACING=2 CELLPADDING=2 ALING=CENTER>\n ");
print ("<TD ALIGN=CENTER VALIGN=TOP>elija</TD>\n ");
print ("<TD ALIGN=CENTER VALIGN=TOP>nombre</TD>\n ");
print ("<TD ALIGN=CENTER VALIGN=TOP>especialidad</TD>\n ");
print ("<TD ALIGN=CENTER VALIGN=TOP>fono</TD>\n ");
print ("</TR>");
while ($roww = mysql_fetch_array ($do)){
print ("TR ALIGN=CENTER VALIGN= TOP\n");
echo "<input type=\"checkbox\" name=\"id\" value=" $roww['nom_medic'] ">";
print ("<TD ALIGN=CENTER VALIGN= TOP>" . $roww['nom_medic'] . "</TD>\n");
print ("<TD ALIGN=CENTER VALIGN= TOP>" . $roww['especi_med'] . "</TD>\n");
print ("<TD ALIGN=CENTER VALIGN= TOP>" . $roww['fono_med'] . "</TD>\n");
}
print ("</TD>\n");

mysql_close ($link);
print ("</TABLE>\n");

?>