Maybe you could consider using something other than telnet? RSH isn't pretty and there are security issues, but telnet has security issues that are just as bad if not worse. At least with rsh you wouldn't be sending the password cleartext.

If your stuck with telnet for some reason, you might want to consider the Expect module for Perl. I've gotten some serious mileage out of that module and even though it has some limitations it's quite nice for connecting to devices that don't have another mechanism for interacting. I've used it to talk to terminal servers, Nortel DMS switches, and I'll probably have to use it talk to an Alteon load-balancer sometime soon too.

With the Expect module you can log in, and look at what you're getting back and adjust your expect statements accordingly. Or since Expect allows you to match using regexes, you can probably devise a regex that covers all the cases you need.

The Expect module is available on CPAN, btw and here are some docs. Good luck!