Siep Kroonenberg reports that there is a package tex4ht http://www.cse.ohio-state.edu/~gurari/TeX4ht/ that converts TeX and LaTeX to various flavors of XML. Currently, its support for DocBook output is limited. If you want to use tex4ht in its current state for LDP you will probably have to hack your LaTeX source beforehand and the generated XML afterwords.