We describe an interactive multimodality display environment, which combines anatomic CT, MRI, functional MRI images and photographs taken during surgical procedures, to provide comprehensive localization information regarding epilepsy seizure foci and the context of their surroundings. Our environment incorporates several unique features, including GPU-accelerated volume rendering and image fusion, versatile GPU-based clipping of volumetric images, and the ability to enhance the information delivered to the surgeon by fusing a direct (photographic) view of the surgical field with the volumetric image. We employ direct volume rendering for the fusion of multiple volumes using GPU-accelerated ray-casting. In addition, to expose the internal structures during volume fusion, we have developed user interaction tools that enable the surgeon to explore the fused volume using clipping-cube and cutaway clipping schemes. The fusion of intraoperative images onto the image volume allows enhanced visualization of the surgical procedure sites within the surgical planning environment. These techniques have been implemented as Visualization Toolkit (VTK) classes using the OpenGL fragment shading program and Python modules, and have been successfully implemented within our surgical planning environment "EpilepsyViewer". The results and performance of our GPU-based approach are compared with similar techniques in VTK, demonstrating that the use of the GPU can greatly accelerate visualization and enable increased flexibility of the system in the operating room. The result of photographic overlay shows good correspondence between the intraoperative photograph images and the preoperative image model. This environment can also be extended for use in other neurosurgical planning tasks.