If the program takes input from STDIN and outputs to STDOUT, the "cheap" way is to just put your program in /etc/inetd.conf, if you are using inetd, or by using something more sophisticated and secure like 'tcpserver' from Dan Bernstein a.k.a. DJB.

For a more "Perly" approach, you have to redirect both STDIN and STDOUT to the socket:

!/usr/bin/perl

use strict;
use IO::Socket::INET;

my $sock = new IO::Socket::INET (
                LocalPort => 5555,
                Listen    => 128,
                Type      => SOCK_STREAM,
                Proto     => 'tcp'
        );

unless ($sock)
{
        die "Could not create socket. Port might be in use.\n";
}

for(;;)
{
        my $new_sock = $sock->accept();

        if ($new_sock)
        {
                unless (fork())
                {
                        $new_sock->autoflush(1);

                        open (STDOUT, "<&=".$new_sock->fileno());
                        open (STDIN,  "<&=".$new_sock->fileno());

                        exec ("program");
                }
        }
}
[download]

You will note that this code has some "issues" which can be resolved by tweaking your socket to be more like a terminal. This, as they say, is left as an exercise for the reader.