Are the new Pentax digitals (K100D etc) compatible with the lenses of the old ME Super?

in short yes

In long, If they have the green "A" on their aperture collar they will run full automatic (except focus). If the do not then you can't use the auto modes, but can still use manual and aperture priority.

You can also use the m42 (screw) mount lenses with a cheap <$25 adapter, you'll be full manual though.

If you plan on using the old lenses you will have to go into the custum setting of the camera to allow use of the aperture ring

Yes.

Since Pentax has the "Shake Reduction" in the body it will work with the older non-auto focus lenses. I think that is a major advantage. The K10D is the latest addition to the line.