Ok, here's my problem, I've got an idea in mind for a game. Problem is, is that I don't want members of the same team to kill each other. I need away to disallow it. Is there away to do that with XMLspawners?

is this using the xmlpoints system? If so then the answer is yes, that is how most of the team games already work.

Ok, new question... how do I create a custom game?

I would just copy one of the gauntlet scripts for the game that is closest to what you are thinking of, and then just rename it and modify the rules by going through the various methods in the gauntlet script and adjusting them to your needs.
You would also copy the gump script for the game and modify that.

It should be fairly easy.