If you want to apply new texture sets you've made, you load them onto the clothes in the Surfaces palette and then save a material preset from the Save as menu, under File or the + icon at the bottom of the Content palette when viewing a D|S content folder.

If you want to model new clothes, you can't yet do that without Poser - we are still waiting on the rigging tools that will allow you to turn a single solid mesh into a posable figure..