[code]
<form id="form1" name="form1" method="POST" action="index.php">
<input type="text" id="trefwoord">
<input type="submit" id="submit">
</form>
<?php
  if( $_SERVER['REQUEST_METHOD'] == 'POST' )
{ 
while mysql_fetch_array($sql) {
$dbveld = $row['veld1']; 
} 
$zoek =  $_POST['trefwoord']; 

$uitvoer = preg_replace('#(' . trim($zoek) . ')#i', 
                  '<span style="color:#666666;"><b>$1</b></span>', 
                  $dbveld); 
?>
<table>
<tr>
<td><?php echo $uitvoer ?></td>
</tr>
</table

<?php 
} 
?>