here is what I get when I run the 
  ./configure --with-mysql --with-apache=../apache_1.3.20 --enable-track-vars :


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
19:19:23~/php-4.0.6

of course after this error, the 'make' command cannot run  

mysql and php are the only modules which I try to compile with apache 1.3.20

could this 'lex output' be because of my OS or from the php source? should I try to install a older version of PHP?
I asked some people but they never encounter this kind of problem before. I hope you did, and solved it ;)

thank you