to install pathan 1

[eric]

Dear Ubuntu experts:
  I am on ubuntu10.04(kernel2.6.38-10)
  I search web about whether there is simple way in ubuntu to install
pathan 1, but so far I can not get.  Need your help.
  so, I also tried old way.
  I download pathan 1, 
but at first stage of configure, I got error
--------
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my xercesc directory is in /usr/include/
and my pathan 1 directory contain the following files:
----

root at eric-laptop:/home/eric/cppcookbook/ch14/download/libpathan-1.0# ls
aclocal.m4    docs         Makefile          runConfigure
autotools     examples     Makefile.defs.in  src
configure     lib          objs              util
configure.in  LICENSE.TXT  README            Win32Projects
----------at configure stage-------
checking unicode support in flex... configure: error: not found. Pathan
requires a version of flex supporting the -U (16-bit unicode) flag.
--------
but I already install flex
need expert's help
thanks a lot in advance, Eric