Indicating Submit button

[David]

Hello.

I have such problem:
On my web form I have one textbox and two buttons (server side ASP buttons),
when I put cursor in this textbox one of the buttons is specified as default
(it becames like activated with rectangle) button, so when I press "Enter"
key this key is pressed.
This is done automatically, but sometimes when I'm designing web form there
is wrong button activated as default button.
How can I control this feature and specify which button must be default?

P.S. When I look in HTML source of running form there are both buttons as
"Submit".

Thank you.