<?php
echo "<select name='nom_plaza'>";
mysql_connect (localhost, root);
mysql_select_db (lloguer);
$result = mysql_query("SELECT DISTINCT nom_plaza from plaza ORDER BY num_plaza");
print ("<option selected>Seleccione una categorÃa</option>");
while ($myrow = mysql_fetch_array($result))
{
echo "<option value='$myrow[nom_plaza]'>$myrow[nom_plaza]</option>";
}
echo "</select>";
?>
take a look at this...