Starting with MacTelnet 4, use of AppleScript with MacTelnet is strongly deprecated. Its replacement will be the new Python-based Quills interface, which is more suitable as a foundation, and more capable of handling some specific needs.
This decision was ultimately made to create a better starting point for future scripting enhancements. AppleScript is still a Mac-only technology, which limits its accessibility to potential extension developers. It also required a non-trivial amount of work to tie into application code, all to support one non-portable language (as opposed to the SWIG approach, where most of the work is not specific to any one scripting language).
Please go to the Quills page for more information!
Python for AppleScript Users
I recommend the simple tutorial written by Aurélio Marinho Jargas if you want to see how AppleScript and Python compare.
You can also visit the main Python site for some excellent documentation.
If you would like to start using Python to drive other applications that are technically AppleScript-based, you can: see the Apple web page on the subject or the appscript project.
Python has a huge standard library that is well documented online. There are also lots of examples included with Mac OS X in the /Developer/Examples/Python tree (if developer tools are installed).