<form method=POST action=/news/admin_news.php?action=doupload enctype=multipart/form-data>

<fieldset>
<legend>Categorie</legend>
<select name=categoria ><option value=aaa>aaa</option><option value=bbb>bbb</option></select>
</fieldset>



File da caricare:

<input type=file name=file size=30>
<input type="hidden" name="categoria" value=bbb>


<button name=submit type=submit>
Upload
</button>

Così può andare?