I have heard that campy 9 and shimano 9 speed are interchangeable.
How interchangeable are they?

Can I use campy shifters and shimano der with shimano casette? Or do I need the campy der as well.

Thanks
Nick

Campy 10 shifters can operate an otherwise all shimano drivetrain with reasonable accuracy, if the shift cable is routed correctly.

http://www.hubbub.com/ergoleverswshim9.htm

The cog spacing on Shimano 9 cassettes is not the same as a campy cassette, so using a campy 9 shifter and derailleur together with a shimano cassette will yield mediocre results.

If it was me, I'd buy campy 10 shifters, rear derailleur, chain and a conversion cassette and move up to 10 speed. Buying new 9 speed campy parts would be a mistake.

Mixing 9sp Shimano and Campy will not work at all. Using a Campy 10 to run 9sp Shimano, is closer to working, but still not all that great. Use one of these to get the cable pull spot on.

http://jtekengineering.com/shiftmate.htm

I have heard that campy 9 and shimano 9 speed are interchangeable.
How interchangeable are they?

Can I use campy shifters and shimano der with shimano casette? Or do I need the campy der as well.

Thanks
NickCog spacing is .2mm different. It works well enough for Sheldon Brown and others, if you use the campy shifters and RD with a shimano casette. or shimano 9 shifters/RD with a campy 9 casette.