Is it hard and how would i go about making a model or live person turn to dust and blow away?

i also need to model the ground cracking.

Thanks,
Stewie

There are so many ways of doing this--it really depends on what you want the final effect to look like. You could, for example, use a material to transform the model's surface into something sandy-looking, then use a boolean cutter with particles + wind to make it look like the model is dissolving. But that's just one idea. You could also make use of a material effector like this: http://johnl.inform.net/pages/matteffect.htm

My advice would be to decide how you want it to look, sketch it out, then solicit some specific plans of attack. It's complicated, but not impossible...

same idea, but more random. This is the shot, haven't descided if i am using a model or an actor.

I want them to be blown away by a wind after having there form turn to dust. or possibly just drop and have the dust fall to the ground. the scene will only be a few seconds long like 10s or so.

That sounds like a two-parter. One step is to transform a model into a dust heap; the next is to make the dust heap blow away. You'll definitely need to use particles.