You can't move values on the On_Load event because during the On_Load event the fields havn't been filled with data yet. The sollution depends on what your trying to do, but one way is to set an After_Update event on the first textbox so that when you set something into it, the VBA code behind the event can easily place what you type into the box into the second text box.
If you want it to automatically load at form load you could try and see if this works. Use the On_Load to trigger the start of the On_Timer event, and give it a few seconds to finish loadin and then let the On_Timer event load the data. It would take a little fine tuning to make this seem seemless. You would probably also want to program it so that after the On_Timer event sets the field it will cease to repeat. I've never used this event so I can't give any details but it could be a good place to start playing.