Flex...

Hello, i ask to the listo for a problem.. and they say me that i havent flex.. yhe error is this.. when i put ./configure to install PHP it says ... checking lex output file root... ./configure: lex: command not found configure: error: cannot find output from lex; giving up i go to www.gnu.com and i download " flex " i descompres it and put ./configure and then make.. but e=when i went to put make install .. it say that the file doesnt exist.. y put dir and there wa a files call " install " if anybody can help me.. please.. help... mi english is very bad... im from argentina.. Bye..and thank you