I configured php 4.2.1 as a dynamic module for Apache 2.0.36 (./configure --with-apxs2=/usr/local/apache/bin/apxs --quiet) and proceeded to make and make install without problems.
After adding the proper entries to httpd.conf, I tried to start Apache and got:

# /usr/local/apache/bin/apachectl start
Syntax error on line 230 of /usr/local/apache/conf/httpd.conf:
Cannot load /usr/local/apache/modules/libphp4.so into server: dlopen: /usr/local/apache/modules/libphp4.so: symbol "__pthread_self" unresolved
/usr/local/apache/bin/apachectl start: httpd could not be started
Exit 3

Here's some info from httpd:

# /usr/local/apache/bin/httpd -V
Server version: Apache/2.0.36
Server built:   May 31 2002 14:29:30
Server's Module Magic Number: 20020329:1
Architecture:   64-bit
Server compiled with....
 -D APACHE_MPM_DIR="server/mpm/prefork"
 -D APR_HAS_MMAP
 -D APR_HAVE_IPV6
 -D APR_USE_SYSVSEM_SERIALIZE
 -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT
 -D APR_HAS_OTHER_CHILD
 -D AP_HAVE_RELIABLE_PIPED_LOGS
 -D HTTPD_ROOT="/usr/local/apache"
 -D SUEXEC_BIN="/usr/local/apache/bin/suexec"
 -D DEFAULT_ERRORLOG="logs/error_log"
 -D SERVER_CONFIG_FILE="conf/httpd.conf"

# /usr/local/apache/bin/httpd -l
Compiled in modules:
  core.c
  mod_access.c
  mod_auth.c
  mod_include.c
  mod_log_config.c
  mod_env.c
  mod_setenvif.c
  prefork.c
  http_core.c
  mod_mime.c
  mod_autoindex.c
  mod_asis.c
  mod_cgi.c
  mod_negotiation.c
  mod_dir.c
  mod_actions.c
  mod_userdir.c
  mod_alias.c
  mod_so.c