How to set Enter Key for Default on Dialog Button

I would like to let the user press the Enter Key on my Modal Dialog
default button (right most button at the bottom???):
Example: I have two buttons defined 'Login' and 'Cancel' listed in
the .dialog in this order -- rendered as 'Cancel' and then 'Login' on
UI. When the dialog is open I want the 'Login' button to be default if
the user presses the 'Enter Key'.
How do I do this?
Thanks,
Marv