Regarding interchangeability...all 8-speed should be compatible with the different freehub body versions of itself. The 9sp shift levers will not be compatible with the 8sp levers, but you can replace the cam to make it compatible with the gear number you want (8,9). I have yet to open up a set of 10sp levers though, so I'm not too sure what they look like inside....probably the same with a few modifications as the 8 and 9sp models.
I would think you can use a 9sp rea derailleur on the 8 speed drivetrain as long as you swap over the pulleys...I'm not sure how much more narrow the rear der. cage is on the 9sp from the 8sp.
Front derailleur comes with an insert to make the cage narrower as well...never tried to pop that off either, nor have I used it with an 8sp drivetrain.
I'm not sure on the 8sp compatability with the freehub body, but I think my hubs are compatible with 9 and 10...same hub body...its a 10sp campagnolo group and I got it a short time after it was first introduced, and never tried putting an 8sp cassete on it, exa or not.
someone please correct me on the information above.