Disable=no is ok. As for the ip's it accepts connections from just define your network in the appropriate line.Define it like 192.168.150.0, for example
(My ipop3 file doesn't seem to have such a line, but I don't use it anyway)
Don't forget to restart xinetd after editing the file, and keep looking at /var/log/messages (use the tail command for that) while testing. It may give some idea of what's going on.
Anything odd in /etc/hosts.allow or /etc/hosts.deny?