How do I create rain in Torque TGEA_1_7_1?

#1 I thought that F5 was the keybind for the Particle Editor?

But it doesn't matter because Rain is not a particle effect but a Preciptation fx object. In "~/scripts/server/environment.cs" you'll find a bunch of datablocks that setup properties for things like rain, snow, and duststorms.... maybe even lightning. In "~/data/environment" you'll find some funny looking graphic images with about 16 rain/dust/snow drops on each one.

So long as you have these datablocks and the correct graphics all you need do is open up the World Editor (F11), switch to the Creator Panel (F4) -- lower right side of the screen, Mission Objects -> Environment -> Precipitation -> select one of the Precipitation data Datablocks from the drop-down box -> and there will be your precipitation effect.

Once you've done that switch back to the Inspector Panel (F3) and in your scene tree find the precipitation object that you just created. Inside of it you'll find some properties of that you can tweak/alter/change.