flex not found

Hi Folks, I have just tried to install PHP4 on a Storm Linux installation and everytime i run ./configure --with-apache=/usr/local/apache but the config fails saying checking for flex...no checking foe lex...no ./configure: flex: command not found checking for flex...lex checking for yywrap in -ll...no checking lex output file root... ./configure: lex: command not found configure: error: cannot find output from lex; giving up Can someone give me any pointer son what to do know and how to fix it? Many thanks in advance Neil