DOCBOOK: sect1 in preface

Hi all,

Various probs indeed:
1) xref does not seem to recognize referencies to mediaobject, nor
imageobject, nor imagedata. nsgmls is OK, but jade complains that the
system does not recognize this.
	- How can I achieve that?
	- If so, are figures automatically assigned a number?
2) though sect1 is told to be accepted as a children of preface, nsgmls
tells me the following:

nsgmls:/usr/lib/sgml/CATALOG:49:0:W: DTDDECL catalog entries are not
supported
nsgmls:ess.sgml:4:14:E: document type does not allow element "SECT1"
here
nsgmls:ess.sgml:5:6:E: document type does not allow element "PARA" here
nsgmls:ess.sgml:8:8:E: end tag for "SECT1" which is not finished
nsgmls:ess.sgml:9:13:E: end tag for "PREFACE" which is not finished   

for this sample code:

<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V3.1//EN" >
<book>
    <preface>
        <sect1>
	<para>
	Some content is always required.
	</para>
	</sect1>	
    </preface>
</book>

	- Why?

Thanks, Camille.