Assuming that your mod_perl-enabled server listens to port 8080, telnet to your server at port 8080, type HEAD /HTTP/1.0, and then press the Enter key twice:
panic% telnet localhost 8080 HEAD / HTTP/1.0
You should see a response like this:
HTTP/1.1 200 OK Date: Mon, 06 May 2002 09:49:41 GMT Server: Apache/1.3.24 (Unix) mod_perl/1.26 Connection: close Content-Type: text/html; charset=iso-8859-1 Connection closed.
Server: Apache/1.3.24 (Unix) mod_perl/1.26
confirms that you have mod_perl installed and that its version is 1.26.