PHP4 - configure errors (bison, lex and flex not found)

Hi I'm a Linux newbie trying to configure PHP4.0.3 with mySQL support on Linux Mandrake 7.1. I've installed Apache and mySQL ok but the configure instructions I am following for PHP fail with the messages below. I would be grateful if anyone could explain (in simple language please!) what I need to do. Many thanks Graham loading cache ./config.cache checking for a BSD compatible install... /usr/bin/install -c checking whether build environment is sane... yes checking whether make sets ${MAKE}... yes checking for working aclocal... missing checking for working autoconf... missing checking for working automake... missing checking for working autoheader... missing checking for working makeinfo... missing checking whether to enable maintainer-specific portions of Makefiles... no checking host system type... i686-pc-linux-gnu checking for gawk... gawk checking for bison... no checking for byacc... no checking for gcc... gcc checking whether the C compiler (gcc ) works... yes checking whether the C compiler (gcc ) is a cross-compiler... no checking whether we are using GNU C... yes checking whether gcc accepts -g... yes checking how to run the C preprocessor... gcc -E checking for AIX... no checking for gcc option to accept ANSI C... none needed checking for ranlib... ranlib checking whether gcc and cc understand -c and -o together... yes checking whether ln -s works... yes checking for flex... no checking for lex... no checking for flex... lex checking for yywrap in -ll... no checking lex output file root... configure: warning: You will need bison if you want to regenerate the PHP parsers. ./configure: flex: command not found ./configure: lex: command not found configure: error: cannot find output file from lex; giving up