Here you go! Here is how to connect that old TU to a PC with a RS-232 serial port. http://www.eham.net/articles/7305
BTY, it's not a TNC! It has a demodulator, tone generators for mark, space, and CW, and three filters. Two filters of which are used for the mark and space tones and one for a CW tone at 700 Hz. It also has a nice tuning display but it's easy to mistake the space tone peak instead of the desired mark tone. No big deal after you play with it tuning in a few stations. The article pretty much shows you everything you need to know. Terman93 is good software for RTTY, Amtor, and Pactor I modes and yes, full ARQ capability! Something you just can't get with a sound card. You can also hook it up to use it with Hamcomm 3.1 software and even WF1B RTTY contest software works with it.
I think I can find the manual for it and can scan it and attach the resulting PDF file to a email back to you if you like. 73 and good luck!