Steph's reply is correct - the button with focus always responds to the Enter key. But if no button has focus, i.e. the focus is on a non-button component such as an edit box, then if one of your buttons has its Default property set to True, it will respond to the Enter key. My guess is your second button is probably the "Default" button - check its properties. You may want to set it to False.
If you always want the first button to respond to the Enter key even if a non-button component has the focus at the time, then set the first button's Default property to True.
Mark