I expect it says "Poser's Material Room". I would imagine you can easily add new images through the Surfaces palette in DS - open it (View>Tabs>Surfaces), switch to the Surface selection tool (Tools>Surface selection) and click on the backdrop; now in the Surfaces palette click on the bar under the Difuse colour colour picker bar (it may already have an image name if the item loads textured) and pick an image that came with the item or one of your own that matches the requirements in the readme; that should do the job, at least at a basic level, so just switch back to your regular posing tool 9Tools menu, or use one of the toolbar buttons) and carry on as usual.