perlpop has a few prerequisites:
perl 5.6.1 (or above)
and a couple of modules, inculding: IO::Socket::INET and IO::Multiplex
If either of these modules are not on your system, you can easily get
them by searching on http://search.cpan.org.

cp perlpop.pl /usr/local/script
chmod 755 /usr/local/script/perlpop.pl
chown root /usr/local/script/perlpop.pl

You now have to choose how to start perlpop.  You can either 
configure your startup scripts to start it for you, or, I'd recommend
running perlpop under DJB's daemontools (available at:
http://cr.yp.to/daemontools.html )

Notes:
DEBUG = set to 1 to send more output to logs
CHID = the user to change to after creating socket on port 110
MYNAME = a name to tell SMTP clients your hostname is
LISTEN_IP = IP Address to listen on (0.0.0.0 will listen on all)
CHKPW_PROG = program to pipe credentials to (checkpassword compatible)
PWD_PROG = program that will give the present working directory (pwd)
APOP_PROG = program similar to CHKPW_PROG that supports APOP
INTERVAL = interval in seconds clients must wait between POP attempts
           (0 or null disables checking)

#### FOR STARTUP SCRIPTS ONLY ####
edit the contrib/rc.perlpop, and set the variables as needed
 cp contrib/rc.perlpop /etc/rc.d/perlpop
(or cp contrib/rc.perlpop /etc/rc2.d/S99perlpop)
make sure you set up a cron to cp /dev/null /var/log/perlpop.log

#### FOR DAEMONTOOLS ONLY ####
edit the contrib/daemontools/run file, and set the variables as needed
 mkdir -p /service/perlpop/log/ /var/log/perlpop/
 chown nobody /var/log/perlpop
 cp contrib/daemontools/run /service/perlpop/run
 cp contrib/daemontools/log/run /service/perlpop/log/run
 chmod 755 /service/perlpop/run
 chmod 755 /service/perlpop/log/run

####  That's It.

 (for daemontools): tail -f /var/log/perlpop/current
or
 (for startup script): tail -f /var/log/perlpop.log