http://www.jclark.com/sp/sx.htm

SX converts SGML to XML. SX parses and validates the SGML document contained in sysid... and writes an equivalent XML document to the standard output. SX will warn about SGML constructs which have no XML equivalent.


-x xml_output_option

lower
    Prefer lower case. Names that were subjected to upper-case substitution by SGML will be folded to lower case. This does not include reserved names; XML requires these to be in upper-case.

so sx -x lower will do the translation you want,
producing lower case tags.

HTH DaveP

Grtz,
Geert