execute your httpd binary on the commandline with the -l switch
On my box this produces
[root@fire->home|root]# /usr/sbin/httpd -l
Compiled-in modules:
http_core.c
mod_env.c
mod_log_config.c
mod_mime.c
mod_negotiation.c
mod_status.c
mod_include.c
mod_autoindex.c
mod_dir.c
mod_cgi.c
mod_asis.c
mod_imap.c
mod_actions.c
mod_userdir.c
mod_alias.c
mod_access.c
mod_auth.c
mod_setenvif.c
mod_php4.c
Notice the mod_php4.c module that is listed. If you don't have something similar to this, then you don't have php installed.