Saving poser pictures, Right click on inlarged Picture and save as GIF,Then right click on GIF and open in Photoshop ,save in Exports ,Open Z Brush, under Docs Import Image And Modify. 
Not exactly sure what you are getting at Rembrant. Opening up a image created in Poser in Zbrush? If so, the Gif Format is not a very good choice as it is limited to only 256 colors. I would save it as a BMP or a PSD file which is directly importable into Zbrush. My second choice would be JPG and then convert it in Photoshop to PSD or BMP
But the real question is, why not import your poser figure straight into Zbrush as an OBJ file. Southern has some great tutorials on doing just that. Then you can morph, texture and whatknot on a real 3D object right smack dab in Zbrush