The resolution of the Spherical Map HDRIs is 13,196 x 6,598 pixel.
Radiosity- and therefore the use of HDRIs - is directly supported in many 3D-applications like Lightwave (version 6.0 and higher), Softimage|XSI, Maya & Mentalray, Pixar RenderMan, Bryce 6, Autodesk VIZ, messiah:render (Arnold), InSight (Integra), 3ds Max & VRay, 3ds Max & Brazil r/s (Splutterfish), 3ds Max & Cebas finalRender, Cinema4D Version 8.1 and more. For further HDRI-rendering tools options the documentation of the used 3D-program should be consulted.
Each HDR image is provided in the industry standard .HDR. So they are usable in most rendering applications.