Calling MX prototype classes and instances

i’m rockin’ with creating prototype classes, however, i’ve run into something i can’t explain when i am trying to call my prototype classes–in this case, i have a prototype class called interfaceClass, which contains several class functions–i’ve also created an instance of the class, called ‘ui’:

interfaceClass.startGame=function(){
trace(“startGame”);
ui.resetGame();
titleMC.unloadMovie(titleMC);
radar.start();
hiScoreMC.unloadMovie();
interfaceClass.startTurn();
}

in this function, you can see that i call both the instance of the class, as well as calling the function by its class name–this code works, but it doesn’t when i try to swap the method of calling around, ie. i can’t figure out when to call the function using the instance name or the class name–i’d rather not use the instance name, as that makes it less oop–who can help explain the rhyme and reason of this? mucho thanks!

-mojo