onsubmit og link i stedet for submit-knap

Hejsa - jeg kan ikke få en advarsel frem om at bestemte forn-felter ikke er udfyldte. Jeg ved ikke om det er fordi jeg ikke bruger en normal submit-knap... Nogen forslag?

koden:

<form METHOD="POST" ACTION="indsaet_gaestebogindlaeg_handler.jsp" NAME="form" ENCTYPE="multipart/form-data"
onsubmit="if(!this.navn.value || !this.indhold.value) { alert('Der skal indtastes navn og kommentar'); return false; } else return true;">
<style type="text/css">
  textarea {
  scrollbar-3dlight-color: #EFF3FF;
  scrollbar-darkshadow-color: #AFC2E4;
  scrollbar-track-color: #DAE0F1;
  scrollbar-face-color: #AFC2E4;
  scrollbar-arrow-color:  #FFFFFF;
  scrollbar-highlight-color: #FFFFFF;
  scrollbar-shadow-color: #DAE0F1;
 
  }
</style>
<p>&nbsp;</p>
<p>&nbsp;</p>
<center>
<table border="0" cellpadding="0" cellspacing="0" style="border-collapse: collapse" width="302" height="250" bgcolor="#F0F4FF">
  <tr>
    <td width="493" height="19" colspan="3">&nbsp;</td>
  </tr>
 
  <!-- navn -->
  <tr>
    <td width="154" height="25" align="right" valign="top"><b>*</b><font face="MS Sans Serif" size="2">navn</font>:</td>
    <td width="15" height="163" rowspan="5"><br>&nbsp;</td>
    <td width="406" height="25" align="left" valign="top">
    <input TYPE="TEXT" style="background:DAE0F1;border:1px solid black;font:bold 10px verdana;" name="navn" value="" size="26"></td>
  </tr>
 
  <!-- indhold -->
  <tr>
    <td width="154" height="60" align="right" valign="top"><b>*</b><font size="2" face="MS Sans Serif">kommentar:</font></td>
    <td width="406" height="60" align="left" valign="top">
    <TEXTAREA name="indhold" rows="4" cols = "25" style="background:DAE0F1;border:1px solid black;font:bold 10px verdana;"></TEXTAREA></td>
  </tr>
 
  <!-- filnavn -->
  <tr>
    <td width="154" height="28" align="right" valign="top">
    <font size="2" face="MS Sans Serif">billede:</font></td>
    <td width="406" height="28" align="left" valign="top">
    <input TYPE="file" style="background:DAE0F1;border:1px solid black;font:bold 10px verdana;" name="filnavn" size="15"></td>
  </tr>
 
  <!-- email_adresse -->
  <tr>
    <td width="154" height="28" align="right" valign="top">
    <font size="2" face="MS Sans Serif">e-mail:</font></td>
    <td width="406" height="28" align="left" valign="top">
    <input TYPE="TEXT" style="background:DAE0F1;border:1px solid black;font:bold 10px verdana;" name="email_adresse" value="" size="26"></td>
  </tr>
 
  <!-- hjemmeside -->
  <tr>
    <td width="154" height="25" align="right" valign="top">
    <font face="MS Sans Serif" size="2">hjemmeside:</font></td>
    <td width="406" height="25" align="left" valign="top">
    <input TYPE="TEXT" style="background:DAE0F1;border:1px solid black;font:bold 10px verdana;" name="hjemmeside" value="http://" size="26"></td>
  </tr>
 
  <!-- SUBMIT -->
  <tr>
    <td width="493" height="30" colspan="3" valign="bottom" align="justify">
    <font face="MS Sans Serif" size="2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <a href="#" OnClick="document.form.submit();">Skriv i
    Gæstebogen</a></font><BR></td>
  </tr>
 
 
  <tr>
    <td width="493" height="38" colspan="3"><b>
    <font size="2" face="Times New Roman"><br>&nbsp;<font color="#3366CC">
    </font><font color="#89A4E2">*</font></font><font face="MS Sans Serif" size="2" color="#99B1E6">
    </font></b><font face="MS Sans Serif" size="1" color="#99B1E6">navn og kommentar skal
    udfyldes :)</font></td>
  </tr>
</table>
</center>
</form>