Fomail validering

Hej E......

jeg har denne formmail.

<table cellpadding="0" cellspacing="0" border="0" width="474" height="">
<tr>
<td width="50"><FORM action="http://scripts.wannafind.dk/form2mail.asp" method="post" name="formen">Navn :</td><td width="424"><INPUT type="text" name="navn"></td>
</tr>
<tr>
<td width="50">E-mail :</td><td> <INPUT type="text" name="adresse"></td>
</tr>
<tr>
<td valign="top">Besked :</td><td><TEXTAREA name="blah" rows="10" cols="45"></TEXTAREA></td>
</tr>
<tr>
<td></td>
<td>
<INPUT type="hidden" name="recipient" value="questis@questis.dk">
<INPUT type="hidden" name="fromaddress" value="questis@questis.dk">
<INPUT type="hidden" name="subject" value="kontakt">
<INPUT type="hidden" name="redirect" value="http://www.questis.dk/questis/tak.htm">
<INPUT type="hidden" name="orderby" value="navn,adresse,blah">
<INPUT type="submit" value="Send">

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

</td>
</tr>

</table>

man hvordan gør jeg så den validere :
navn: minimum 2 tegn
E-mail: for at @
og besked for minimum 20

mvh.
questis.dk