Moment of Inertia Calculation for Conic Disc with Hole in Center

[CBrandi]

Hi everybody.
I'm a newbie here.
I'm a Physics student at University of São Paulo in Brazil (I'm in 1st year) and find this forum was a very nice surprise for me. I think this is the best thing about Physics in all web and I would like give all of you my congratulations.
Well, my doubt is about Moment of Inertia.
I need calculate the moment of inertia for a conic disc with a hole in the center according the figure below. I made several searches on Internet and didn't find nothing about this.
The diametral section of the ring is like following:
http://img178.imageshack.us/img178/7999/discocnico013ai.jpg
Thank you very much.

 

[Doc Al]

set up the integral

Realize that the contribution of a given mass element to the moment of inertia is $r^2 dm$. Hint: Treat the object as composed of a set of concentric rings. Write "dm" for these rings as a function of r and the density. Integrate!