Nadya,

In the Gotfocus Of the container you set teh defautl proeprty of the button to .F. and in the keypress of each textbox you put;

IF nKeyCode = 13 && Enter
   IF EMPTY(This.Value)
      NODEFAULT
      Thisform.MethodCalledByTheDefaultButton
   ENDIF
ENDIF

In the LostFocus of each textbox you put:

Thisform.DefaultButton.Default = .T.

You might want to add a property to the textbox class to hold the name of the default button so it isn't hardcoded.