Check your /etc/inetd.conf file to make sure those services are enabled there. You should be able to compare the malfunctioning machine's file with a working machines file. Mine are in the "other services" section.
If you are using a firewall on the dial-up router, you might have something in your ipchains/iptables rulesets that is blocking these ports. Worth a check. Cheers, -Don Spoon-
