Dropdown update zonder pagina refresh

Graag zou ik willen weten hoe ik een 3 textboxen kan vullen vanuit een dropdown menu zonder een refresh van de pagina. Ook de "Selected value" moet worden getoond in de dropdown. Ik weet dat dit via ajax kan, maar dit lukt mij niet.

Als voorbeeld de aangepaste versie van het bestand:

<?php

/* URL: /page.php?do=reparatieverzoeken&p=7&rep_id=799&id=533 */

/* UPDATE STATEMENTS VERWIJDERD


/* #################################################
START PAGINA REPARATIEVERZOEK_UPDATE.PHP
################################################# */


print "<table border=\"0\" cellpadding=\"1\" cellspacing=\"1\">
<tr><td colspan=\"2\" class=\"title\">Wijzigen reparatieverzoek </td></tr>
<tr><td width=\"88\"><img src=\"img/leer.gif\" width=\"88\" height=\"4\"></td>
<td width=\"450\"><img src=\"img/leer.gif\" width=\"450\" height=\"1\"></td></tr>
<tr><td colspan=\"2\"><img src=\"img/lines/l738.gif\" width=\"738\" height=\"1\"></td></tr>
<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"8\"></td></tr>
</table>

<table border=\"0\" cellpadding=\"1\" cellspacing=\"1\">";

$rep_id=$_GET['rep_id'];

/* VULLEN VAN DROPDOWN LEVERANCIER */
$sql2= "SELECT id,naam FROM ".DB_PREPEND."tblLeverancier ORDER BY naam";
$rs2 = mysql_query($sql2) or die(mysql_error());
/* EINDE VULLEN VAN DROPDOWN LEVERANCIER*/

$query1 ="SELECT * FROM ".DB_PREPEND."tblReparatieverzoeken, ".DB_PREPEND."tblLeverancier WHERE tblLeverancier.id = tblReparatieverzoeken.rep_leverancier AND rep_id = $rep_id";

$resultaat = mysql_query($query1) or die(mysql_error());
// $aantal = mysql_num_rows($resultaat);

while ($gegeven = mysql_fetch_object($resultaat)) {

$rep_leverancier = $gegeven->rep_leverancier;
$naam = $gegeven->naam;
$fax = $gegeven->fax;

print "<form method=\"post\" action=\"page.php?do=reparatieverzoeken&p=7&rep_id=$rep_id&rep_opdrachtnr=$rep_opdrachtnr\">

<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"5\"></td></tr>
<ta<tr><td align=\"left\" class=\"error\">Algemene gegevens&nbsp;</td></tr>
<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"5\"></td></tr>
<tr><td colspan=\"2\"><img src=\"img/lines/l738.gif\" width=\"738\" height=\"1\"></td></tr>

<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"10\"></td></tr>
</table>

<table border=\"0\" cellpadding=\"1\" cellspacing=\"1\">
<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"10\"></td></tr>
<tr><td align=\"left\" class=\"chatlist\">Leverancier&nbsp;</td>
<td><table border=\"0\" cellspacing=\"0\" cellpadding=\"0\"></tr>

<tr><td><select name='rep_leverancier'><option selected value=\"$rep_leverancier\">$naam</option>";

while($row2 = @mysql_fetch_array($rs2))
{
Print "<OPTION VALUE=\"$row2[id]\">$row2[naam]</OPTION>";
}
print "</select></td><td>&nbsp;&nbsp;</td></tr>

</table></td></tr>


<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"10\"></td></tr>
<tr><td align=\"left\" class=\"chatlist\">Contactpersoon&nbsp;</td>
<td><table border=\"0\" cellspacing=\"0\" cellpadding=\"0\"></tr>
<tr><td><input name=\"contact\" value=\"$contact\" type=\"text\" class=\"f11b\" id=\"contact\" style=\"width: 300px\" size=\"40\" maxlength=\"30\"></td><td>&nbsp;&nbsp;</td></tr>
</table></td></tr>

<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"10\"></td></tr>
<tr><td align=\"left\" class=\"chatlist\">Fax&nbsp;</td>
<td><table border=\"0\" cellspacing=\"0\" cellpadding=\"0\"></tr>
<tr><td><input name=\"contact\" value=\"$faxnr\" type=\"text\" class=\"f11b\" id=\"contact\" style=\"width: 300px\" size=\"40\" maxlength=\"30\"></td><td>&nbsp;&nbsp;</td></tr>
</table></td></tr>

<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"10\"></td></tr>
<tr><td align=\"left\" class=\"chatlist\">Email&nbsp;</td>
<td><table border=\"0\" cellspacing=\"0\" cellpadding=\"0\"></tr>
<tr><td><input name=\"contact\" value=\"$email\" type=\"text\" class=\"f11b\" id=\"contact\" style=\"width: 300px\" size=\"40\" maxlength=\"30\"></td><td>&nbsp;&nbsp;</td></tr>
</table></td></tr>

<tr><td colspan=\"2\"><img src=\"img/leer.gif\" width=\"1\" height=\"10\"></td></tr>

<table>

<tr><input type=\"hidden\" name=\"rep_id\" value=\"" . $gegeven->rep_id . "\"> </td>
<tr><td><input name=\"submit\" type=\"Submit\" type=\"submit\" class=\"button10\" value=\"OK\" >
<input name=\"donotsubmit\" type=\"button\" class=\"button10\" value=\"Annuleren\" onClick=\"location.href='page?do=reparatieverzoeken&amp;p=1&amp;rep_id=$rep_id'\"></td></tr>
</table></form>";

}

php?>

Jim