Hello,
I've done a synopsis of the first part of Gradus on my website,
at http://homepage.eircom.net/~gerfmcc.
The site includes Java applets which allow you to enter your own
counterpoint to each cantus firmus which Fux provided in each of the five species. I had to take down species 2 thru 5 applets but they'll be back up within a week. The applets will analyse your counterpoints
and provide comments on their conformance to Fux's rules.
I've got to say I loved Gradus, Fux's attitude to pedgogy shines through,
he must have been a fine teacher. Whatever you think about it as a
compositional instruction manual, it is unquestionably one of the classic
texts in musical literature. It must say something that Bach, Haydn,
Beethoven, Strauss and Hindemith are among those who are known to have had high regard for it.