[xsl] Transforming a non-hierarchical XML into a hierarchical one

[SEXpeare <sexpeare@xxxxxxxxx>]

Hello everybody, I have to transform a non hierarchical XML:

	<sumario>
		<seccion txt=""/>
		<subseccion txt=""/>
		<organismo txt=""/>
		<anuncio txt=""/>
		<organismo txt=""/>
		<anuncio txt=""/>
		<organismo txt=""/>
		<anuncio txt=""/>
		<subseccion txt=""/>
		<organismo txt=""/>
		<anuncio txt=""/>
		<seccion txt=""/>
		<subseccion txt=""/>
		<organismo txt=""/>
		<anuncio txt=""/>
		...
	</sumario>

into a hierarchical XML, doing this via XSLT. The result must be like this:

	<sumario>
		<seccion id="">
			<subseccion id="">
				<organismo id="">
					<anuncio>
					</anuncio>
					...						
				</organismo>
			</subseccion>
		</seccion>
		...
	</sumario>

I would apreciate any idea or advice, thx.