RobotC doesn't have a program chooser, instead you have to select your teleop file in RobotC itself in the window where you can drive the robot.
You have to download your autonomous routine(s) to the NXT brick first. Then after connecting via the FCS, you select the autnomous routine that you want to run before placing your robot on the field. Assuming the template has been used correctly (which can be downloaded
here), you can then tell your robot to run its autonomous routine by pressing the start match button. After the end of autonomous, when you tell your robot to begin teleop, it should run the teleop file that you selected to run earlier in RobotC itself (this file should still be downloaded on the brick though). We were told at our first scrimmage that you now have to run RobotC version 2.0, so make sure you've downloaded that.