There was a book sold by Universal radio (don't know if they still have it) that showed you how to read the messages. I kinda doubt you could get one from ARINC/SITA as they aren't real fond of hobbyists being able to read these messages.
However other packages such as ACARSD do decode most of the messages into English, at least the old version I used to run. Might be worth considering if you want to stay with this. It's freeware....73 Mike
I know that program, it's good but get with BMT first, he is a member here & extremely helpful. He has a serious aviation set-up at his qth, if you are really serious about this, he will hook you up big time, or should I say, real time. Good luck.
I guess that does keep you busy. Sounds exciting. What kind of equipment are you working with? I'm just getting back into it after many years (and a divorce) . Just trying to catch up with the new systems and trying to find some new thing to monitor.
apd, if you want something 'new to monitor', stick your nose in the Maryland sticky thread on Milcom. There is quite literally a ton of information to be had here - lots going on, all the time. Your PRO-97 and 2004 will do for a start; you didn't say what antenna(s) you are using, but getting a discone, ScanTenna or one of the DPD Productions antennas up in the air will open up a new world for you. The 2004 may need a little 'kick in the pants' via a preamp, as it's not as sensitive as many of the newer scanners, but it's pretty flexible. I had one for a number of years, but got rid of it a year or two ago as it had a bad volume control pot that I couldn't find much of a replacement for.
We have a LOT of information on milcom monitoring in our area in the wiki, although some of it could stand some updating. Most of the frequency information there is still pretty good, though. I will send you a list of articles to read up on in a private email, since this post is technically OT....73 Mike