Continued help with RPG Game

I own and administrate a MMO RPG Game [login to view URL] I have recently had a new area added, but I am having problems with one part of the PHP code working properly. In this area, players 'bet' money against one another.? I need the code to be able to take money 'crystals" from a player as they enter the fight arena.? The money that they are willing to bet will go in a graph that has already been made, it just will need another column added to it.? When someone clicks on the <fight> icon, I need money "crystals" to be taken from the other person as well.? Then the winner will be given the crystals at the end of the fight. I do not believe in the right hands this would be a difficult task to complete.