There was a discussion on the Houdini forums that I took part in that I thought was worth not just one video tutorial but a three part series. I think it’s a really simple task but shows oh so much and is easily applicable to more complex work. What it covers is taking an object that will emit particles and dictating what points on the emitter send out particles and in what direction using a bounding object and one of the bounding object’s normals. You can find the videos and completed .hipnc file here.
Here is what the final result looks like (note that I changed the resulting file a bit to get a good flipbook result):