default button in content section with master pages

asp.net 2.0

I have several image buttons for the main navigation on my master page. One
of my content pages is for loging in and has a login button on it under the
user name and password boxes (it's a slightly modified asp.net 2.0 login
control but that shouldn't matter as far as I know for this problem). I
would like the login button on the content page to be the default button but
no matter what I try, the topmost button of my navigation buttons is always
activated. I tried puttign the login control in a panel but that did
nothing. The main navigation button still was activated. I cannot change the
navigation buttons from image buttons. I went been through a lot of grief to
get them to work. They are rollover buttons. They used to be href's (wint
img's in them) but I had to chagne them to image buttons to so that I could
use relative paths in the urls in order to make them work when the user is
on a page that is in a subfolder. It was a mess. That part works great now
and I understand why it didn't before. But when they were href's the login
button behaved as the default since it was the only actual button on the
page. Now that's not the case and I'm stuck again. I don't mind making the
user have to "click" the login button but it's pretty annoying when you
enter your login info and hit "Enter" and then you are not logged in and
taken back to the home page. What can I do to solve this?

Thanks,

Keith