You have to put values using the SmartDashboard class
For example
http://wpilib.screenstepslive.com/s/...-robot-program
SmartDashboard only looks at a single table in networktables so that you can use other tables to send data to other programs but not have it show up on the SmartDashboard
You can also find more info on the SmartDashboard here
http://wpilib.screenstepslive.com/s/3120/m/7932