Yes to 1, often just with scaling on x/y/z, or "stretching" it over a different figure by scaling the figure flatter at the beginning of the simulation.  Some trial and error required.

Sometimes to 2, but often conforming clothes are not modeled and imported into Poser in such a way that this is easy; often parts of the clothing is not weldted together, and it will fall to pieces once you treat it as dynamic.  

If your dynamic clothing intersects anything it collides against when you start the simulation, then chances are it will not be too productive to go forward; Poser semi-tries to force the intersected bits back outside of collision area but often it mangles the mesh of the cloth very badly.  Best to get as close a fit as reasonable before you run the simulation.  It's usually okay if the cloth is a bit too big though, and often very helpful to just scale down your figure in one or more axes just to make things easier.

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