Or remotely...

telnet 127.0.0.1 80
HEAD / HTTP/1.1
[download]

(you should substitute an the ip address of the machine in interest for 127.0.0.1 in this example) The should reply something like

HTTP/1.1 400 Bad Request
Date: Tue, 17 Sep 2002 23:32:19 GMT
Server: Apache/1.3.26 (Unix) Debian GNU/Linux mod_gzip/1.3.19.1a mod_p
+erl/1.27 DAV/1.0.3
Connection: close
Content-Type: text/html; charset=iso-8859-1

Connection to host lost.
[download]

Note the presence of something like mod_perl/1.27 says that mod_perl v1.27 is running in Apache.