If you modelled the dress to loosely fit the character, just import it into the Poser, and position it around the character, just like you modelled it. (Or if you modelled it around the character and your scaling is right, in Posrt it will come in in the same spot as when modelled)

The rest of the process of making it dynamic happens in Poser's cloth room. Your best bet is to search for Poser's cloth room totorials.

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