Alt-Az tracking apart from field rotation also does not smoothly track stars, its steped because both Alt and Az need to change. Where as with an RA-DEC, once you are on the object only your RA needs to counter the earths rotation. With minor tuning of DEC.
This is a good demo.
http://science.howstuffworks.com/telescope5.htm
It has also been reccomended to me by my mates that i might look at an Alt-Az motorisation and then add wedge like device for polar alignment. Specifically the Mel Bartel system. And being in IT i am sure i can locate a few old Floppy drives.