Can't build gem -- native extension -- can't find installed library function

I can't figure out what is going wrong here -- any ideas??

I'm running on a Ubuntu 8.04 LTS, and have installed libxml2 and libxslt from these instructions:

http://www.techsww.com/tutorials/libraries/libxml/installation/installing_libxml_on_ubuntu_linux.php

http://www.techsww.com/tutorials/libraries/libxslt/installation/installing_libxslt_on_ubuntu_linux.php

However, I installed the latest versions:

libxslt-1.1.24
libxml2-2.7.3

The install was uneventful


-------------------- I set LD_LIBRARY_PATH ----------------------------------

echo $LD_LIBRARY_PATH
/usr/local/libxslt/lib:

-------------  seems like the function is present -- at least based on the output of strings ------------
/usr/local/libxslt/lib$ strings * | grep ParseStylesheetDoc
xsltParseStylesheetDoc
xsltParseStylesheetDoc
xsltParseStylesheetDoc
xsltParseStylesheetDoc
xsltParseStylesheetDoc
xsltParseStylesheetDoc
xsltParseStylesheetDoc

----------------------- But the compile still fails   ----------------------------------------

sudo gem install webrat
Building native extensions.  This could take a while...
ERROR:  Error installing webrat:
      ERROR: Failed to build gem native extension.

/usr/local/bin/ruby extconf.rb install webrat
checking for iconv.h in /opt/local/include/,/opt/local/include/libxml2,/opt/local/include,/opt/local/include,/opt/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/include,/usr/include/libxml2... yes
checking for libxml/parser.h in /opt/local/include/,/opt/local/include/libxml2,/opt/local/include,/opt/local/include,/opt/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/include,/usr/include/libxml2... yes
checking for libxslt/xslt.h in /opt/local/include/,/opt/local/include/libxml2,/opt/local/include,/opt/local/include,/opt/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/include,/usr/include/libxml2... yes
checking for libexslt/exslt.h in /opt/local/include/,/opt/local/include/libxml2,/opt/local/include,/opt/local/include,/opt/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/local/include,/usr/local/include/libxml2,/usr/include,/usr/include/libxml2... yes
checking for xmlParseDoc() in -lxml2... yes
checking for xsltParseStylesheetDoc() in -lxslt... no
libxslt is missing.  try 'port install libxslt' or 'yum install libxslt-devel'
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
      --with-opt-dir
      --without-opt-dir
      --with-opt-include
      --without-opt-include=${opt-dir}/include
      --with-opt-lib
      --without-opt-lib=${opt-dir}/lib
      --with-make-prog
      --without-make-prog
      --srcdir=.
      --curdir
      --ruby=/usr/local/bin/ruby
      --with-iconv-dir
      --without-iconv-dir
      --with-iconv-include
      --without-iconv-include=${iconv-dir}/include
      --with-iconv-lib
      --without-iconv-lib=${iconv-dir}/lib
      --with-xml2-dir
      --without-xml2-dir
      --with-xml2-include
      --without-xml2-include=${xml2-dir}/include
      --with-xml2-lib
      --without-xml2-lib=${xml2-dir}/lib
      --with-xslt-dir
      --without-xslt-dir
      --with-xslt-include
      --without-xslt-include=${xslt-dir}/include
      --with-xslt-lib
      --without-xslt-lib=${xslt-dir}/lib
      --with-xml2lib
      --without-xml2lib
      --with-xsltlib
      --without-xsltlib


Gem files will remain installed in /usr/local/lib/ruby/gems/1.8/gems/nokogiri-1.3.3 for inspection.
Results logged to /usr/local/lib/ruby/gems/1.8/gems/nokogiri-1.3.3/ext/nokogiri/gem_make.out