Same error upgrading from Etch to Lenny on i686 (Core2 Duo). Worked around the issue by running the following two commands.
update-xmlcatalog --del --type public --id '-//OASIS//DTD DocBook XML V4.1//EN' --package docbook-xml update-xmlcatalog --del --type public --id '-//OASIS//DTD XML Exchange Table Model 19990315//EN' --package docbook-xml -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]