You need to wrap the options field in a show if statement. In other words if Product size > 0 then show the field otherwise keep it hidden.
<?php if ($totalRows_rsSizeOptions > 0) { // Show if recordset not empty ?>
<td>Size:</td>
<td>
<label>
<select name="SizeOptions" id="SizeOptions">
<option value="">Please Select</option>
<?php
do {
?>
<option value="<?php echo $row_rsSizeOptions['ColoursID']?>"><?php echo $row_rsSizeOptions['ColourName']?></option>
<?php
} while ($row_rsSizeOptions = mysql_fetch_assoc($rsSizeOptions));
$rows = mysql_num_rows($rsSizeOptions);
if($rows > 0) {
mysql_data_seek($rsSizeOptions, 0);
$row_rsSizeOptions = mysql_fetch_assoc($rsSizeOptions);
}
?>
</select>
</label>
<br />
<?php } // Show if recordset not empty ?>