Attached Link: http://brian.curiouslabs.com

Dunno if this answers your question but there is a motion blur document under the Render menu in Poser 5 (sorry, I don't user Poser 4 anymore). After you complete your render, you can use this feature to create 2D motion blur on a still image. I don't think it will create a blurred background. You must use depth of field for that or F-stop, focal distance as mentioned above. All mentioned are worthy suggestions. -Brian