Okay. This may sound a little odd, but One:is it possible to make a weapon that creates a shield on whatever it hits, and Two: is it possible to make a shield that prevents anything from leaving it, but things can enter?

1. I don't think so, unless you could settle for a weapon that spawns a geometry temporarily.

2. That depends... Do you want it as a trap sort of? Just thinking out loud, but someone could make a "Shield" model, with a collision, that is not "closed" in the back, people could walk through one side of the collision, but not the other.

1) Yes, but what do you mean by shield? The way I'm thinking, it would be the same shield as used in the Holocron game mode.
2) Assuming you can create an entity with the properties you want, I know how to get it to the correct location ingame. Err, I'm thinking you mean some sort of trap weapon? You fire it, and an one-way shield forms around whatever you hit (could be yourself). Or did you want to place the one-way shield in ZeroEdit?

Both deal with weapon hit detection, meaning you will need to use that 'took damage' even callback (its correct name is in the scripting doc).