I've found a wonderful way to install Apache with PHP on a help document from php3.info .... it is as follows ... BUT I've not installed the default Apache and PHP from the slackware CD, it's all done from source.
1. gunzip apache_1.3.14.tar.gz
2. tar xvf apache_1.3.14.tar
3. gunzip php-4.0.3pl1.tar.gz
4. tar xvf php-4.0.3pl1.tar
5. cd apache_1.3.14
6. ./configure --prefix=/usr/local/apache
7. cd ../php-4.0.3pl1
8. ./configure --with-mysql --with-apache=../apache_1.3.14
10. make install
11. cp libs/libphp4.a ../apache_1.3.14/src/modules/php4/
12. cd ../apache_1.3.14
13. ./configure --activate-module=src/modules/php4/libphp4.a
15. make install
Changing version numbers as needed.
The original is here
Thanks goes to Stephen VanDyke ( stephen at opido dot com ) for posting this on the php site in the first place. This seems to work fine for me, so if you have problems let me know.