When connecting to minerva and other such computers, you must use SSH (secure shell) rather than telnet. Both telnet and SSH are terminal emulation protocols. Unlike telnet which is considered insecure, SSH encrypts all data, including passwords, so that your traffic cannot be intercepted (sniffed) by other network users.
There are a number of SSH clients available, including NiftyTelnet SSH for the Macintosh, PuTTY and TeraTerm Pro SSH for Windows, and OpenSSH for UNIX-variant operating systems. In Mac OS X, the command ssh is available in the Terminal application by default, or you may which to install JellyfiSSH. (The Terminal application is located in the Utilities folder in Applications; open the Terminal application and type ssh minerva.simons-rock.edu).
Much of this software may be found on the CMS software website at http://cms.simons-rock.edu/software/. Alternatively, there is a web-based Java SSH client that you can use at http://www.simons-rock.edu/ssh/.