The problem is that the HIP is the master bodypart in Poser. And then you have two legs which should suddenly be co-joined - meaning the bodyparts will.. well.. be odd.

So going Dynamic is the easiest way. There are skirts out there with lots of morphs to simulate movement, and I assume the morphs can be linked to the legs with ERC. There's also skirts with "Body handles" (bodyparts without actual geometry) to help movement.

Depending on what you need it for (animation or just stills) you might be able to put the necessary morphs into it - or use the Cloth Room (this of course requires Poser 5 or higher)

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.