BIG problem...

Hello.. i speak spanish so.. i prefear the answer to this question will in spanixh: I have a problem... i do all correctily but.. iy happens.. a lot of times.. : bash-2.04# cd apache_1.3.19 bash-2.04# ./configure --prefix=/www Configuring for Apache, Version 1.3.19 + using installation path layout: Apache (config.layout) Creating Makefile Creating Configuration.apaci in src Creating Makefile in src + configured for Linux platform + setting C compiler to gcc + setting C pre-processor to gcc -E + checking for system header files + adding selected modules + checking sizeof various data types + doing sanity check on compiler and options Creating Makefile in src/support Creating Makefile in src/regex Creating Makefile in src/os/unix Creating Makefile in src/ap Creating Makefile in src/main Creating Makefile in src/lib/expat-lite Creating Makefile in src/modules/standardb bash-2.04# cd php-4.0.6 bash-2.04# ./configure --with-mysql --with-apache=../apache_1.3.x --enable-track-vars 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... found 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 configure: warning: You will need bison if you want to regenerate the PHP parsers. 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... 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 bash-2.04# well .. this is my problem.. i dont now ... if you can get me same help.. thank you....