Had to build lttoolbox on a box running an older verion of Red Hat Enterprise Linux for a demo. I am glad to report that the stable release of lttoolbox builds on Red Hat Enterprise Linux version 4 once the libxml2 packages are upgraded. Currently lttoolbox needs libxml2 => 2.6.17. RHEL4 ships with slightly older version of this library.
Grab these rpm files from the XMLSoft.org sources directory (or elsewhere) and do a upgrade with 'rpm -U ' command.