But in some cases, the Dom is more userful than SAX, with some google research, i found the API of TouchXml, http://code.google.com/p/touchcode/.
It solved the problem to use NSXmlDocument in the applicatons. Don't forget to check out all source files and add 2 parameters in project.
OTHER LINKER FLAGS = -lxml2
HEADER SEARCH PATHS = /usr/include/libxml2