You're off down a dark, dark path to confusion if you create 3D pie charts - or any other chart type in 3D with only a few exceptions.
Pie charts aren't great at teh best of times but making them 3D makes them useless; the whole point of a pie is to allow you to compare segment sizes; making it 3D skews the perspective making that comparison impossible and inaccurate.
Take a look at the attached document by Stephen Few.
Hope it sheds some light.
All the best,
Matt - Visual Analytics Ltd
Qlikview Design Blog: http://QVDesign.wordpress.com
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