Before you can work with the modules outlined by Taran you'll have to edit the file: httpd.conf to make sure that the module has been loaded. The line you're looking for will read: LoadModule headers_module path/to/mod_headers.so
Then you must include an AddModule directive such as (in your case) :- AddModule mod_expires.c
I have to be very honest here, and say that unless you are truly desperate to do this work I would leave well alone. Configuring Apache servers is not exactly a walk in the park, and there are far more interesting ways of spending an evening. Sad people like Taran and me have to do it for a living, and we might get some sort of satisfaction from it, but frankly I would rather watch a good film any day.