I have a Dewalt DW945 cordless drill, that I had to take apart to fix.
I couldn't get the chuck off, so I had to pry it open at the back, and
I had a hard time putting the case back togther. It seems to be back
together, but the chuck doesn't turn when the motor does anymore,
so I guess I should take it apart again. This time I would like to
take the chuck and the ring behind it off first but I don't know how.

There is no screw to loosen in the bottom of the chuck (unless it is
missing already), and I see no way to hold the shaft in place while I
turn the chuck. I don't even remember which way to turn the chuck to
unscrew it. Clockwise maybe, when looking from the front??

(I've looked at the Dewalt site and elsewhere on the web to try to
answer these questions, but no luck.):

Also what is a versa-chuck? I guess it has something to do with the
numbers 0-11 around the ring behind the chuck. I know I don't have
another one, and I know I want one, but I don't know what it is.

Also, it has both drill and screwdriver settings with a slide thing on
the top, but it also has I and II settings with a slide thing on the
bottom, and I don't know what those mean.