For the RTT cmake to integrate a xerces library installed on a non standard path (eg /opt/xercesc), I had to apply the following patch:

--- ../orocos-rtt-1.8.0-ori/config/check_depend.cmake 2009-02-05 14:35:50.000000000 +0100
+++ config/check_depend.cmake 2009-02-18 13:10:52.000000000 +0100
@@ -33,6 +33,11 @@
ENDIF (NOT CMAKE_CROSS_COMPILE )
IF ( XERCES AND XERCES_HEADERS)
MESSAGE("-- Looking for Xerces - found")
+ SET( RTT_CFLAGS "${RTT_CFLAGS} -I${XERCES_HEADERS}" )
+ GET_FILENAME_COMPONENT(XERCES_LIB_PATH ${XERCES} PATH)
+ LINK_DIRECTORIES(${XERCES_LIB_PATH})
SET(OROPKG_SUPPORT_XERCES_C TRUE CACHE INTERNAL "" FORCE)
LINK_LIBRARIES(xerces-c)
SET(ORODAT_CORELIB_PROPERTIES_MARSHALLING_INCLUDE "\"marsh/CPFMarshaller.hpp\"")