How can I calculate fast!! shadow volumes??

In real time?

If you''re doing all the clipping and capping stuff for near plane projection, you might want to switch to far plane projection instead (google for Carmack reverse shadow).

If you''re developing for high-end hardware, you could try vertex shaders.

By far the best method is to reduce the number of polys casting shadows. Use low LOD models for shadow casters, and only accept objects as shadow casters if they contribute a lot to the scene. Yes, it''s a lot of content management work.