"Well, Stewer would know more than I, since he uses Pixels3D, but I believe the form of IBL it uses is the same as the one that's in Poser 5 right now." Pixels has the Sky Dome feature which allows you to load a regular image as a light map. It does support 16bit TIFF files, so depending on your definition of "high dynamic range" it could qualify as full HDRI IBL. I know, the feature description on the Pixels page sounds a little weak, but basically it is what probably most of you would expect from an IBL solution: Load an image and use that as lights in your scene.