PassiveTeX is a library of TeX macros which can be used to process 
an XML document conforming to the Formatting Objects (FO) spec.
This provides a relatively easy mechanism to convert FO files to
Postscript and PDF.

For example, to generate a PDF file from an FO file, run

    pdftex --interaction nonstopmode "&pdfxmltex" file.fo

WWW: http://www.tei-c.org.uk/Software/passivetex/