ESCs do not use they type of PWM that analogWrite produces.
To control ESCs you will need to use the servo library, this generates the correct signal expected by and ESC or Servo.
Have a look though some of the articles on this page for background info -
about halfway down you will find a section of links to articles about interfacing with RC Equipment and further down some info about th servo library and using it to drive servos or ESCs.
Duane B