Following the below steps will install the latest liblouisutdml tar ball
from http://code.google.com/p/liblouisutdml/downloads/list

NOTE: I am assuming that you already have liblouis installed in /usr
or /usr/local. 

1. Download pkg-config from

  http://pkg-config.freedesktop.org/releases/ Release 0.22 seems to work 
best.

Uncompress it and switch to the newly created directory. Install it
with

  ./configure; make; sudo make install. 

This will install it in /usr/local by default.

2. Add the following line to your ~/.profile (you can change the
system profile if you prefer):

export PKG_CONFIG_PATH="/usr/local/lib/pkgconfig:/usr/lib/pkgconfig"

This line tells configure where to look for the *.pc files for
installed libraries. You should check to make sure that both of these
directories exist. Both of these directories will be needed because
libxml2 comes installed in /usr/lib, and the liblouis library will by
default install in /usr/local/lib.

3. Download the latest liblouisutdml tarball from

  http://code.google.com/p/liblouisutdml/downloads/list
; decompress it; switch to the liblouisutdml directory and run

  ./configure; make; sudo make install

This works on my mac, and so hopefully should work for you.

If you run into linking problems it might be that there are multiple
versions of libxml2 installed. In that case uninstall all of the
libxml2 versions except for the one in /usr/ and try again.

If libraries have been installed in nonstandard locations, then those
pkgconfig paths should be added to the PKG_CONFIG_PATH variable in
~/.profile.