I would start by:
1. Add the blank emitter to the stage (“New Emitter” from the blank.IL3 library).
2. Right click on the emitter, and click Properties, which will bring up the emitter properties window.
3. Click on the particle in the tree on the right (labeled “New Particle Type” in the blank library).
4. In the Particles tab in the middle of the window, uncheck the box marked “Use emitter’s emission angle and range”.
5. Click on the “velocity” property in the tree on the left. In the Behavior tab, in the graph window, slide the value for frame 1 up to about 110.
6. Click on the “emission angle” property in the tree on the left (this didn’t exist until you unchecked the box in step 4). Adjust the slider for frame one up to 90. You’ll now have particles streaming straight up.
7. Add points at different frames to the emission angle, and adjust each point up or down, to make the stream go in arcs left or right.
On that last step, you’ll have to experiment with different frames and angle values to get the look you want. I expect you’ll also want to change the particle image. I’d look at the Water Faucet emitter in the water_01.IL3 library; that one works best if you set some motion blur.
I left out some basic how-to’s in the above steps, but you ought to be able to pick up the basics from the tutorial docs that come with PI.
Hope that helps. 🙂