How to enable button?

I have a html form. It has two buttons. I want without
mouse click if <Enter key> is pressed by default one 
of them to work.

Currently if I press enter none of them works.

Is there any TAB ORDER concept in HTML form?

Can I do something in Form OnLoad function to
give enter key focus to the one of the button.

For example in following page http://home.microsoft.com/
if click on hotmail logon/password edit box.
The enter button gets <Enter Key> focus.

I will appreciate any kind of help on this.

-ravi