I am a beginner in Houdini. I just went through the rendering tutorial. I found mantra's area lights work very well! but it seems that Houdini's area lights are only for Mantra. If I use prman (in Houdini) to render area lights or softshadows, does that mean I have to duplicate many lights(instance) to simulate?

Does anyone have any idea of a good way of how I can render soft shadows and area light in Houdini with rman?

Look at the Renderman Application Notes distributed with Renderman on Area shadows and Min/Max shadowmaps.