I began using Pro-tools simply because it was the "industry standard" and when I began working in the studio, I wanted to get some extra practice. Unfortunately, I use it more for recording audio than MIDI. Our in-house track maker is more Keyboard based rather than Computer based in his sequencing, so we just dump the tracks as audio into pro-tools or as a stereo track and then add the recording.
It is a very good program, however I have my own issues with the hardware compatibilty. If you're looking to learn the program rather than buying something new, I'd suggest the following book:
Pro Tools 6 for Macintosh and Windows (Visual QuickStart Guide)
https://www.amazon.com/exec/obidos/ASIN/0321213157/qid=1106170985/sr=2-3/ref=pd_ka_b_2_3/103-3875589-5106266
You can usually get it used for under $10 and it has really been a lifesaver for me, I have one at home and one at the desk in the studio.
Also, Digidesign has a User Conference you can join through their website that is specifically geared to which pro-tools system you have as well as what OS you're using.
Hope this helps, sorry I couldn't be more informative
Justin