Allá va el código del form:
<form name="frmUploadImg" method="post" action="a_uploadimage.asp" onSubmit="javascript
: return frmCheck();" enctype="multipart/form-data">
<input type="hidden" name="producto" value="<%=valor%>">
<table align="center" border="0" cellpadding="1" cellspacing="1" width="100%">
<tr>
<td>
<table align="center" border="0" cellpadding="1" cellspacing="1" width="100%">
<tr><td colspan="4" class="tdCabecera1" style="border-bottom: solid 2px #000000;">UPLOAD IMAGEN</td></tr>
<tr>
<td width="9%" height="61" class="tdCabecera4">Fichero</td>
<td><input type="file" name="upfichero" size="30"></td>
</tr>
<tr><td colspan="20"> </td></tr>
<tr>
<td align="center" colspan="4">
<input type="submit" value="Aceptar">
<input type="button" value="Volver" onClick="javascript
: location.href='i_webimagelst.asp';"> &n bsp;
</td>
</tr>
</table>
</td>
</tr>
</table>
</form>