Any question answered...

*Campagnolo's spline configuration is not the same as Shimano's, and. Campagnolo has repeatedly modified it.
Many replacement parts are not available for older models. Most Campagnolo cassettes will work on Campagnolo hubs made for larger numbers of sprockets.
*Cog spacing is different enough from Shimano's that Shimano derailers and shifters may not work well with Campagnolo cassettes, and vice versa.
It is possible to fudge compatibility in some cases where cog-to-cog spacing is similar**.

http://www.sheldonbrown.com/k7.html#spacing