Untar them, and run the configure program on Apache like so.
./configure --exec-prefix=/usr \ --localstatedir=/var \ --mandir=/usr/share/man \ --libexecdir=/System/Library/Apache/Modules \ --iconsdir=/System/Library/Apache/Icons \ --includedir=/System/Library/Frameworks/Apache.framework/Versions/1.3/Headers \ --enable-shared=max \ --enable-module=most \ --target=apache
If you want the compiler to do some optimization, you may also want to add this line:
setenv OPTIM=-O2
Next, go to the PHP 4 source directory and configure it.
./configure --prefix=/usr \ --sysconfdir=/etc \ --localstatedir=/var \ --mandir=/usr/share/man \ --with-xml \ --with-apache=/src/apache_1.3.12
If you have any other additions (MySQL, GD, etc.), be sure to add them here. For the --with-apache string, put in the path to your apache source directory, for example /src/apache_1.3.12.
Now, reconfigure Apache to build in PHP 4.
./configure --exec-prefix=/usr \ --localstatedir=/var \ --mandir=/usr/share/man \ --libexecdir=/System/Library/Apache/Modules \ --iconsdir=/System/Library/Apache/Icons \ --includedir=/System/Library/Frameworks/Apache.framework/Versions/1.3/Headers \ --enable-shared=max \ --enable-module=most \ --target=apache \ --activate-module=src/modules/php4/libphp4.a
You may get a message telling you that libmodphp4.a is out of date. If so, go to the src/modules/php4 directory inside your Apache source directory and run this command: ranlib libmodphp4.a. Then go back to the root of the Apache source directory and run the above configure command again. That'll bring the link table up to date. Run make and make install again.
cp php.ini-dist /usr/local/bin/php.ini
or (if your don't have a local directory)
cp php.ini-dist /usr/bin/php.ini
.