[drfknd]

Hello,
how do I create a pie chart like this:

http://start1.jpl.nasa.gov/images/techPieChart.gif

using OmniGraffle?

I can't connect a line between the midpoint of a circle and its edge...
And if I just put several lines above the circle, then I can't colour
the pies.

Try the adjustable wedge shape in the Shapes collection under Window > Stencils.

[drfknd]

I have tried that. But I find it almost impossible just to create a pie chart consisting of four equally-sized pies...

Try the pie chart script here:

http://www.petermcm.dircon.co.uk/software/