The cloth does not have to be rigged. The cloth editor in Poser allows you to designate the properties of cloth vertices either singerly or in groups as to their relationship to the figure. Similar to collision detection plugins in high end 3D modelers. As the animation progresses the editor then uses those cloth vertice's to interact in relationship with the solid figure or object.

PS: This dress was modeled in Rhino to fit the Poser figure. It was then imported to Poser and arranged. Both the figure and dress were brought into the cloth editor.

A high poly count helps in defining how well the cloth reactes with the solid object but also slows the computer down because it cherns more vertices in the process.