From LightWiki

Go to Dynamics>Dynamic Objects>Particle.

Choose Partigon for the Particle type.

Change the Generator> Size to 10m x 1m x 10m.

Go to the Etc>Gravity and change it to -9.8 in the Y direction. Move this emitter to 10m in the Y.

Now add a Dynamics>Dynamic Objects>Collision item set to Plane. Set its Mode to Erase and its Radius/Level to 0. As the particles hit the collision, they'll die.

Add another Particle emitter of Partigon type and Parent it to your 'rain' emitter. Change its Nozzle to Parent-emitter(End) This tells the emitter to emit at its parents particles' positions when they die.

This can create a lot of particles, so set the Birth Rate to 10, and THEN the Generate by to 'Frame'. We do that second because 100 particles a frame can quickly kill your system.

The particles won't look like much because a lot of them are being erased too, so go to the Motion Tab and set the Velocity to 10m/s in the Y axis.

This causes them to just go up, so set Vibration(m/s) to 5 and this will disperse them.

Finally, go to the Etc tab and set Gravity to -9.8 in the y to see your raindrops turn into splashes.

You can change the surface of the Partigons in the Surface Editor and the size of them in the Object Properties Panel in the Edges tab, under Particle/Line thickness. To get them to motion blur turn on Particle blur in the Camera Properties Panel.