You can do this up to a point, by using Jtek ShiftMate
http://jtekengineering.com/shiftmate.htm, but looking briefly through their combinations, using 9 Speed Campag Shifters and RD with an 8 speed Shimano cassette looks to be one of a few combinations they don't support.
From what you have said you have 3 options
1, if you stick with the 8 speed Shimano cassette you could either get a ShiftMate #2 and an 8 speed Shimano RD
2, You mentioned a 9 speed Shimano cassette, if you get this, use a ShiftMate #1
3, just get a Campagnolo rear wheel / cassette (this is the option I would use)
You would need to decide what is most cost effective option for yourself.