Is there any tutorial or site that teachs special effect modeling like NUCLEAR EXPLOSION? For example, observing C&C General, many explosion or special effects are not simply by particle-engine... I guess it is modeled by some tools... I am trying to imitate that effect, but it is not easy to me... So, I want to some tips to model it... please help me...

They're particles though, you can generate those easily with particle engine in content creation packages, what you can do though is pre-rendered them, and just display them as simple animated billboard.

that is what a particle engine is for. The particles are usu. generated via path controls and emiters to generate new particle types (like transition from explosion to smokes)...etc...etc. There are various places here in gamedev.net that has particle engine tutorials and such.

you have made the first step, anyalizing other peoples work
is a good way to a start special effect. I would also look for similar effects in films and real footage of what you want to produce.

Creating effects with a particle engine is not always easy,
ideally you need to tailor your engine/editor to what you
want to produce. A good example of a flexible particle editor
would be max payne 2's. Doom3 has a reasonable particle editor
which you can access from the console. It has some nice features, but maybe not as flexible as I would like