iavap,
Apache has a servlet 2.0 compliant extension called JServ. You can also use Jakarta's Tomcat which is the Open Source reference implementation of the 2.2 level of the servlet API. I believe the plan is to roll Tomcat into Apache and replace the old JServ. You must have at least one of those to enable your Apache to run servlets (though there are many other servlet engines out there some of which also work with Apache).
As far as using servlets from PHP, you can use the PHP servlet extension to run PHP itself in your servlet container (as a servlet). The PHP servlet extension includes the full PHP/Java extension which allows you to invoke any other Java class (including other servlets).
There was an additional article posted lately by Jeremy Monteleone explaining how you can use sockets to invoke servlets and get the results in your PHP code without using the PHP servlet feature.
Alex
